Cocaine is interrelated with the opioid system on many levels, especially via the mu opioid receptor (MOR). Also, cocaine has been involved in modulating nitric oxide (NO) actions within the cell. The effect of cocaine was first assessed on the MOR, and then on transcription by the use of 1 µg/ mL actinomycin D inhibitor. Several signaling pathways that cocaine may exert its action in modulating the MOR up-regulation in protein expression were also explored. Two dosage regimens were used in cocaine treatment, single continuous treatment (SCT), and repeated intermittent treatment (RIT). Different pathway inhibitors were used on PC12 cells, as follows: the PLC-PKC inhibitors 5 µM U-73122 and 10 µM BIS-1 used to investigate the involvement of the PKC signaling pathways in MOR expression levels, the evaluation of MAPK pathway by the use of 50 µM U0126 inhibitor, and the 10 µM LY94002 inhibitor was used to investigate the PI3K/Akt pathway. Moreover, the effect of NO on these signaling pathways was investigated by the use of 20 mM nonselective L-NAME inhibitor and qualitatively by DAF-2 florescence. Western blot analysis indicated that cocaine up-regulated MOR protein expression. Also, RIT cocaine treatment increased MOR protein levels via transcription. All three signaling pathways, MAPK, Akt and PKC modulated cocaine-induced increase of MOR following SCT cocaine treatment (post-transcriptional). Both MAPK and Akt have been found to modulate the cocaine-induced transcription of MOR via the two dosage regimens of cocaine, SCT and RIT. Also, inhibition of both PLC and PKC did not prevent cocaine-induced increase in MOR transcription, according to RIT of cocaine. Furthermore, Akt and PKC appeared to modulate cocaine-induced NO production while MAPK did not. NO seemed to be involved with the PKC and Akt pathways in up-regulating MOR in RIT of cocaine directly by the Akt pathway, and indirectly by the PKC pathway. On the other hand, NO and MAPK modulated the MOR up-regulation expression simultaneously, but in an individual/parallel manner. Furthermore, signaling pathway activation levels were tested using L-NAME which concluded that NO modulated cocaine-induced increase in total Akt protein levels, but did not appear to have an effect on phosphorylated MAPK activation levels. In conclusion, different treatment regimens of cocaine activate different pathways; SCT of cocaine activated all three signaling pathways, however, RIT of cocaine activated only the MAPK and Akt pathways. / Saudi Bureau in Canada

Les principaux analgésiques utilisés en clinique ciblent majoritairement le récepteur opioïdergique mu (MOPR). Or, l'activation de MOPR engendre d'importants effets secondaires. Les agonistes sélectifs au récepteur opioïdergique delta (DOPR) représentent une cible thérapeutique intéressante, puisqu'ils engendrent moins d'effets secondaires comparativement à l'activation du récepteur opioïdergique mu (MOPR). Dans la littérature, 2 hypothèses s'opposent concernant à la fois la distribution de DOPR et de MOPR au sein des sous-populations neuronales ainsi que leur implication fonctionnelle dans certaines modalités de douleurs. D'une part, des études, dont certaines basées sur l'utilisation d'anticorps, ont suggéré une colocalisation de ces 2 récepteurs au sein des mêmes sous-populations neuronales. Cette colocalisation suggère que l'activation de MOPR ou DOPR soulage les mêmes modalités de douleurs. D'autre part, une étude a remis en doute la spécificité des anticorps commerciaux ciblant DOPR, remettant ainsi en question les travaux réalisés avec cet outil. Par ailleurs, les auteurs de cette même étude ont aussi observé une ségrégation physique et fonctionnelle entre DOPR et MOPR : non seulement DOPR et MOPR seraient exprimés par des populations neuronales différentes, mais DOPR régulerait préférentiellement les douleurs d'origine mécanique, alors que MOPR serait plutôt impliqué dans le soulagement des douleurs d'origine thermique. Afin de répondre à cette controverse, il a d'abord été nécessaire de trouver un outil alternatif à l'utilisation des anticorps ciblant DOPR. Idéalement, cet outil doit permettre la visualisation de la distribution de ce récepteur autant au niveau de cellules en culture que des tissus. Pour ce faire, les propriétés pharmacologiques de 2 ligands biotinylés, le TIPP-biotine (Tyr-Tic-Phe-Phe(para-bromoacétamide)-Asp-desthiobiotine) et la deltorphine-biotine, ont été déterminées. Les résultats obtenus ont démontré que le TIPP-biotine possède des caractéristiques de liaison sur DOPR fort intéressantes autant sur des extraits cellulaires que sur du tissu animal, alors que la deltorphine-biotine nécessite encore des modifications afin d'optimiser ses propriétés de liaison à DOPR. Dans un second temps, à l'aide d'études d'électrophysiologie unitaire extracellulaire in vivo et d'immunohistochimies du récepteur NK? (récepteur de la substance P), l'implication de MOPR dans le soulagement des douleurs thermiques et mécaniques, et celle de DOPR dans le soulagement des douleurs mécaniques ont été mises en évidence. [symboles non conformes]

Depuis quelques années, le récepteur opioïdergique delta (DOPR) apparaît comme une alternative intéressante dans le traitement de la douleur puisque son utilisation est accompagnée de moins d'effets secondaires qu'avec les traitements opioïdergiques actuels, ciblant principalement le récepteur opioïdergique mu (MOPR). Par contre, les agonistes sélectifs pour DOPR n'ont que très peu d'effets chez les animaux sains en raison d'une faible expression membranaire du récepteur. Depuis quelques années, un nombre croissant d'études se sont intéressées à l'adressage de DOPR et les résultats montrent que différentes situations peuvent moduler son expression à la membrane plasmique. Mes travaux de Thèse se sont donc intéressés à la régulation de DOPR dans un contexte de traitement de la douleur. En premier lieu, nous avons montré que les agonistes sélectifs pour DOPR soulagent l'hyperalgésie thermique induite par l'inflammation et que cet effet est conservé lors d'un traitement prolongé. À l'opposé, les effets antinociceptifs et moteurs de la deltorphine sont rapidement soumis à la tolérance. La dichotomie observée quant au développement de la tolérance pour les effets des agonistes DOPR suggère que des mécanismes de régulation différents s'opèrent lors de l'activation soutenue de DOPR. Dans un deuxième temps, nous avons montré que des agonistes sélectifs pour DOPR et MOPR, inhibent les comportements douloureux ainsi que l'activation neuronale (c'est-à-dire l'expression de c-fos) induits par la formaline ou la capasïcine. De plus, les agonistes DOPR et MOPR empêchent la relâche de substance P via l'inhibition des fibres afférentes primaires, ce qui confirme leur localisation sur les fibres peptidergiques. Par ailleurs, puisque les agonistes DOPR et MOPR ont des actions similaires sur la relâche de substance P, nos résultats proposent une colocalisation de DOPR et MOPR. L'ensemble de ces résultats contribuent à élargir nos connaissances sur les rôles et la régulation de DOPR dans le but d'en faire une cible thérapeutique pour le traitement de la douleur chronique.

abstract: Intermittent social defeat stress produces vulnerability to drugs of abuse, a phenomena known as cross-sensitization, which is proceeded by a corresponding upregulation of ventral tegmental area (VTA) mu-opioid receptors (MORs). Since VTA MORs are implicated in the expression of psychostimulant sensitization, they may also mediate social stress-induced vulnerability to drugs of abuse. Social stress and drugs of abuse increase mesolimbic brain-derived neurotrophic factor (BDNF) signaling with its receptor, tropomyosin-related kinase B (TrkB). These studies examined whether VTA MOR signaling is important for the behavioral and cellular consequences of social stress. First, the function of VTA MORs in the behavioral consequences of intermittent social defeat stress was investigated. Lentivirus-mediated knockdown of VTA MORs prevented social stress-induced cross-sensitization, as well as stress-induced social avoidance and weight gain deficits. Next it was examined whether VTA MOR expression is critical for stress-induced alterations in the mesocorticolimbic circuit. At the time cross-sensitization was known to occur, lentivirus-mediated knockdown of VTA MORs prevented stress-induced increases in VTA BDNF and its receptor, TrkB in the nucleus accumbens (NAc), and attenuated NAc expression of delta FosB. There was no effect of either stress or virus on BDNF expression in the prefrontal cortex. Since social stress-induced upregulation of VTA MORs is necessary for consequences of social stress, next activity dependent changes in AKT, a downstream target of MOR stimulation associated with sensitization to psychostimulant drugs, were investigated. Using fluorescent immunohistochemical double labeling for the active form of AKT (pAKT) and markers of either GABA or dopamine neurons in the VTA, it was determined that social stress significantly increased the expression of pAKT in GABA, but not dopamine neurons, and that this effect was dependent on VTA MOR expression. Moreover, intra-VTA inhibition of pAKT during stress prevented stress-induced weight gain deficits, while acute inhibition of VTA pAKT blocked the expression of cross-sensitization in subjects that had previously exhibited sensitized locomotor activity. Together these results suggest that social stress upregulates MORs on VTA GABA neurons, resulting in AKT phosphorylation, and that increased VTA MOR-pAKT signaling may represent a novel therapeutic target for the intervention of substance abuse disorders. / Dissertation/Thesis / Doctoral Dissertation Neuroscience 2015

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-07-03T12:46:24Z No. of bitstreams: 1 BrunnaSantanaDeVasconcellos_DISSERT.pdf: 4909084 bytes, checksum: 8df41e0e78db0c16f71dee97eee833b1 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-07-06T15:00:47Z (GMT) No. of bitstreams: 1 BrunnaSantanaDeVasconcellos_DISSERT.pdf: 4909084 bytes, checksum: 8df41e0e78db0c16f71dee97eee833b1 (MD5) / Made available in DSpace on 2017-07-06T15:00:47Z (GMT). No. of bitstreams: 1 BrunnaSantanaDeVasconcellos_DISSERT.pdf: 4909084 bytes, checksum: 8df41e0e78db0c16f71dee97eee833b1 (MD5) Previous issue date: 2017-04-10 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Problemas pr?ticos de controle, comumente, se apresentam com muitas vari?veis a serem controladas simultaneamente e que dependam uma das outras, surgindo, com isso, a necessidade de um estudo aprofundado sobre controle multivari?vel. Analisar a capacidade e a potencialidade de diferentes estrat?gias de controle, buscando as mais adequadas para cada tipo de sistema ? fundamental. Nesse contexto, esse trabalho aborda um procedimento sistem?tico acess?vel de como se projetar um controlador fuzzy eficaz para sistema multivari?veis. O procedimento consiste em dividir o projeto em etapas claras e cont?nuas, nas quais s?o sintonizados os par?metros de controladores fuzzy multivari?veis. A primeira etapa se inicia considerando o sistema com diversas malhas que contenham uma entrada e uma sa?da, os controladores fuzzy sintonizados para cada malha, nessa etapa, s?o iguais aos comumente sintonizados para sistemas SISO; a segunda etapa compreende a uni?o das informa??es dos controladores sintonizados na etapa anterior em um ?nico controlador fuzzy MIMO, que considera todas as entradas e sa?das, mas sem acrescentar ainda a influ?ncia de cada malha nas outras; a ?ltima etapa consiste em incluir essa influ?ncia que cada vari?vel exerce sobre todo o sistema din?mico, por meio da inclus?o de um complemento na base de regras e das fun??es Sugeno de sa?da. Dessa forma, ? poss?vel se ter uma melhor compreens?o e se obter um melhor desempenho do controlador, por ser poss?vel analisar o comportamento do sistema em cada etapa do projeto. Para comprovar sua efici?ncia, o m?todo aqui abordado ? aplicado a diferentes estudos de caso pr?ticos e simulados. Ap?s isso, esse controlador fuzzy multivari?vel ? comparado com outros controladores por meio da an?lise gr?fica e do c?lculo de ?ndices de desempenho para a valida??o do procedimento utilizado. / Control?s practical problems usually appear with lots of variables to be controlled simultaneously. Its biggest problem is that frequently the variables depend on each other, making necessary a deep study about multivariable control systems. Analyze capability and potential of different control strategies is extremely important to get the most appropriate control mode to the system. In this context, this work approaches systematic procedures to project an effective fuzzy controller focused in multivariable systems. It consists in splitting the controller design in three steps, where it?s parameters are synchronized with multivariable fuzzy controllers. The first step considers a system with a single input and a single output. At second step, all the controllers are joined into a single one, with all the inputs and outputs include without accounting each loop influence?s. Last step happens including the influence of each loop on the whole system. This approach makes possible a better performance from the controller, since it?s possible to analyze the system behavior in each step. To prove this procedure efficiency, the method is applied to different cases of study, including practical and simulated cases. The outcome multivariable fuzzy controller is compared with others by using graphical analysis and calculated indexes of performance to validate the chosen procedure.

Most clinical opioids produce analgesia through the Mu Opioid Receptor (MOR) providing the only effective treatment for chronic pain patients. These studies explore three pre-clinical strategies to improve MOR analgesia and minimize side effects: 1) compounds that target G-protein Coupled Receptors (GPCRs) heterodimers, such as heterodimerization between the Delta Opioid Receptor (DOR) and MOR (MDOR); 2) multi-functional compounds that target multiple receptor systems for synergistic effects, such as a MOR agonist and a the serotonin reuptake transporter (SERT) inhibitor; or 3) biased agonists that preferentially activate one signaling pathway associated with analgesia over another associated with side effects at the same receptor. First, several indirect lines of evidence indicate the MOR-DOR heterodimer (MDOR) can regulate MOR opioid tolerance and withdrawal. However, studying MDOR remains difficult because no selective MDOR antagonists are available. To address this need, we created a novel series of bivalent MDOR antagonists by connecting a low affinity MOR antagonist (H-Tyr-Pro-Phe-D1Nal-NH2) to a moderate affinity DOR (H- Tyr-Tic-OH) antagonist with variable length polyamide spacers (15-41 atoms). In vitro radioligand binding and [35S]-GTPγS coupling assays in MOR, DOR, and MDOR expressing cell lines show bivalent ligands produce a clear length dependence in MDOR but not MOR or DOR cell lines. The lead compound – D24M with a 24-atom spacer – displayed high potency (IC50MDOR = 0.84 nM) with 91-fold selectivity for MDOR:DOR and 1,000-fold MDOR:MOR selectivity. Second, clinicians have long appreciated subtle but distinct differences in analgesia and side effects of MOR opioids. A variety of non-MOR targets including DOR, Kappa Opioid Receptor (KOR), the Cannabinoid Receptor-1 (CB1), the Sigma-1 Receptor (σ1R), the Dopamine- (DAT), Serotonin- (SERT) and Norepinephrine- Reuptake Transporters (NET) induce analgesia and/or modulate MOR mediated side effects. To determine if different opioid profiles arise from non-MOR interactions, we evaluated the binding and function of nine clinical analgesics at the nine aforementioned targets revealing several clinical opioids contain previously unidentified affinity’s or activity’s. Hydrocodone displayed low affinity at the MOR (KI = 1800 nM) and only ~2 fold less affinity at the σ1R (KI = 4000 nM). Second buprenorphine promoted monoamine influx at DAT, SERT and NET with EC50 > 1,000 nM. These novel interactions suggest the nuanced differences of clinical opioids may arise from previously unappreciated off-target effects. Future studies will assess whether these in vitro results predict hydrocodone and buprenorphine activity in vivo. Finally, the unique function of the numerous endogenous opioid peptides at a given receptor remains unclear. How endogenous ligands interact with ORs produces obvious drug design consequences. These studies show two endogenous Dynorphin analogues – Dynorphin A and Dynorphin B – differentially regulate two ubiquitous signaling modules – βarrestin2 and Gαi/o– at the DOR. Dynorphin A and Dynorphin B swap potency rank orders for β-arrestin2 recruitment and [35S]-GTPγS signaling, indicating two distinct signaling platforms are formed. Dynorphin A but not Dynorphin B treatment simulated AC super activation, while Dynoprhin B internalized DOR better than Dynorphin A. These in vitro assays suggest endogenous Dynorphin analogues differentially regulate signals at the DOR in vitro. Future work includes further characterizing signaling differences in vitro and testing these changes in vivo.

No description available.

Le Neuropeptide FF (FLFQPQRFa, NPFF) est un neurotransmetteur peptidique, caractérisé par son activité pharmacologique anti-opioïde. Ce peptide active deux récepteurs couplés aux protéines G, NPFF1 et NPFF2. De nombreuses données suggèrent que le NPFF module l'activité opioïde par un effet direct sur les récepteurs opioïdes situés sur les mêmes neurones plutôt que via un effet indirect dû à une modification d'un circuit neuronal. Néanmoins, les mécanismes moléculaires sous-jacents de ce cross-talk entre les récepteurs sont encore mal compris. Ce travail est composé de deux parties principales : 1) les mécanismes anti-opioïdes médiés par les récepteurs du Neuropeptide FF. Nous avons testé les activités directes et anti-opioïdes des récepteurs NPFF sur les canaux calciques voltage-dépendants activés par dépolarisation sur des neurones du noyau raphé dorsal (DRN) de souris. Le récepteurs NPFF dans ces neurones sont préférentiellement couplés aux protéines G de type Gi/o. Les effets directs et anti-opioïdes induits par les récepteurs NPFF interviennent dans des gammes de concentration différentes indiquant que l'activité anti-opioïde spécifique n'est pas une conséquence directe de leur activité sur les canaux calciques. De plus, nous avons comparé ces interactions entre récepteurs NPFF et NOP (nociception, N/OFQ) observés sur des neurones dissociés de souris avec celles observés sur une lignée cellulaire de neuroblastome humain, SH-SY5Y. Les données obtenues en imagerie calcique et dans le test de stimulation de liaison du [35S]GTPyS aux protéines G, montrent un rôle potentiel important des radeaux membrane/lipides (rafts), qui agirait comme une plateforme de signalisation dans les effets du NPFF. 2) le rôle du Neuropeptide FF dans la dépression. Afin de tester le rôle potentiel pharmacologique du NPFF dans la dépression, des injections locales du 1DMe, un analogue du NPFF, ont été réalisées dans le DRN de souris. Nous avons observé une forte activité de cet analogue dans le test de suspension de la queue test et dans le "splash test", comme respectivement une diminution des temps d'immobilité et une augmentation du temps de toilettage. Du fait de l'existence d'un fort effet antidépressif des antagonistes des récepteurs NOP après injection dans le DRN et de l'effet cellulaire anti-N/OFQ du NPFF que nous avons démontré, il est plausible d'envisager que le NPFF possède un effet antidépressif via son action anti-opioïde sur les récepteurs nociceptine. / Neuropeptide FF (FLFQPQRFa, NPFF) is considered as a potent opioid-modulating peptide. It exhibits the opioid-modulation effect by activating two G protein-coupled receptors, NPFF1 and NPFF2. Several observations suggest that the anti-opioid effect of NPFF is more likely mediated by a cross-talk between NPFF and opioid receptors in the same neuron rather than an indirect effect due to a neuronal circuitry. Nevertheless, the precise molecular mechanisms underlying the cross-talk between both receptors remain need to be investigated. This work is composed of two main parts : 1) Neuropeptide FF receptors and the molecular mechanisms of their anti-opioid effect. We tested both direct and anti-opioid activities of NPFF receptors on Ca2+ transient induced by depolarization in mouse dorsal raphe nucleus (DRN) neurons. The NPFF receptor preferentially coupled with Gi/o proteins, which induced the direct activity. Different threshold to observe the direct and anti-opioid effect of NPFF suggested that the specific anti-opioid activity of NPFF receptors was not a direct consequence of their activity on Ca2+ transients. Furthermore, we studied the molecular mechanisms underlying the cross-talk between NPFF and NOP (Nociceptin/Orphanin FQ, N/OFQ) receptors in mouse DRN neurons and SH-SY5Y human neuroblastoma cells. Data from Ca2+ imaging, [35S]GTPyS binding assay and western blot indicated that cholesterol-rich lipid rafts, which acted as a "platform", were involved in NPFF anti-N/OFQ effect, and the siRNA interference data showed that GRK2 protein mediated this process. 2) The potential role of Neuropeptide FF in anti-depressant response. In order to test the potential role of Neuropeptide FF in anti-depression, the NPFF analogue 1DMe was locally injected into mouse DRN. We observed a decrease of immobility time and an increase of grooming time, in tail suspension test and splash test, respectively, after 1DMe treatment. RF9, the specific antagonist of NPFF receptors, reversed the anti-depression effect of 1DMe. Referencing the strong anti-depression effect of NOP receptor antagonists after DRN injection and the cellular anti-N/OFQ activity of NPFF receptors in this nucleus, the hypothesis that the anti-depression effect of NPFF may due to its cellular anti-N/OFQ activity is interesting to be further verified.

No description available.

Initiation of transcription is a major step in the regulation of gene expression. A dominant theme in regulation of gene expression lies in understanding the mechanism involved in selective expression of the genes in response to external or internal stimuli. Gene regulatory proteins bind DNA at specific sites either cognate to the promoters they act upon or at a distance, thereby exerting their effect by turning on (activation) or turning off (repression) the genes. Response of these factors to the environmental signals is further achieved by the DNA binding affinity of the transcription factors that can be modulated by small ligands, concentrations of which may fluctuate in response to nutrient availability and stress. Bacteriophages achieve a high degree of efficiency in gene expression by evolving elegant strategies of transcriptional control. mom gene of enterobacteriophage Mu serves as an excellent model to understand this elaborate regulation of gene expression. The gene encodes a unique DNA modification function that confers an anti-restriction phenotype to the phage genome. Though dispensable for phage growth, it is fascinating in two respects (i) a novel modification; (ii) regulation follows a complex scheme without precedence in prokaryotes. mom is the last gene to be expressed during the phage lytic life cycle. Premature expression of the gene is deleterious to both host and phage and hence it is under a complex regulatory network. Dam methylase, a host encoded protein acts as a positive regulator of gene expression, an example where methylation has been shown to play a positive role in regulating tranascription. OxyR, another host encoded protein negatively regulates mom gene expression. Dam methylation prevents the binding OxyR to its site located in the mom regulatory region. The regulatory interplay also involves two phage encoded proteins. C, a middle gene product is essential for transcriptional switch from middle to late genes and Com, a late gene product, for enhancing translation of mom mRNA. Thus, C and Com serve as transcriptional and translational activators of mom gene expression. Pmom is a weak promoter with both -10 and -35 elements away from consensus and a sub-optimal 19 bp spacer element encompassing a stretch of 6T residues that act as negative elements. ‘T stretch’ is known to induce a kink in the DNA. The sub-optimal spacer region makes the promoter elements out of phase and RNAP by itself cannot bind at mom promoter. C protein exerts its effect in activation in a multistep mechanism. The protein binds DNA as a dimer overlapping the promoter and unwinds the DNA, realigning the promoter elements, thus recruiting the RNAP. In the next step, it enhances the promoter clearance by the enzyme, thus enhancing the rate of productive transcription. With this prevailing knowledge on C mediated mom gene expression, the present thesis work describes the experiments carried out to further understand the molecular mechanism of second step activation at Pmom. Genetic and biochemical analysis were carried out to identify the interacting surface of C protein on RNAP. Subsequently, studies have been extended to understand the C mediated transactivation at other late promoters- lys, I, P, which encode for the lysis and morphogenetic functions of the phage. Finally, Mg2+ coordinating residues in C protein were identified to decipher the ligand induced conformational changes in the activator protein required for its transactivator function. Chapter I, a general introduction to the thesis, deals with the detailed discussion on gene expression and its regulatory mechanisms. RNA polymerase (RNAP) being the central molecule of gene expression (transcription) its organization and assembly are discussed. With the availability of the high resolution crystal structures of bacterial RNAP, an in-depth review on RNAP structure in terms of its potential regulatory targets, conformational changes associated with the formation of a functional holoenzyme, and during its transition from initiation to elongation processes have been described. Regulation of transcription with an emphasis on activation mechanism, ligand mediated allosteric transitions in regulatory proteins and the polymerase-activator interactions are discussed citing a few examples. The chapter concludes by introducing bacteriophage Mu and mom gene and its regulation by C. The objectives of the thesis form the concluding section of the chapter. Activators are capable of resurrecting defective promoters in response to cellular demands. The unusual, multistep activation of mom promoter (Pmom) by C protein involves activator mediated promoter unwinding to recruit RNA Polymerase (RNAP) and subsequent enhanced promoter clearance of the enzyme. The first step of transactivation is an interaction independent step, while the later might involve a transient interaction between C and one of the subunits of RNAP. Previous studies pointed out β′ subunit to be the most probable interaction partner. Chapter II comprises the genetic and biochemical studies carried out to confirm this observation. Employing a genetic screen mutations in rpoC gene (encoding the β′ subunit of RNAP), were isolated which result in the defective RNAP. The mutant RNAPs were assayed for their C specific activity by in vivo transactivation assays. Such mutants have been purified and characterized to understand their effect at different steps of C mediated mom gene expression during transcription initiation. The mutant RNAP had normal transcription activity with typical σ70 promoters but exhibited reduced productive transcription and enhanced abortive initiation on C-dependent Pmom. Experiments carried out to probe the interaction between C and mutant RNAP revealed that the physical interaction per se is not disrupted between the two proteins. Post C-mediated recruitment of RNAP to the promoter, transient interactions between the two proteins appears to induce subtle conformational changes in RNAP leading to an enhanced promoter clearance. Transactiavtor protein C is essential for the expression of other late genes lys, I, P apart from mom during the phage life cycle. Although the mechanism of multistep activation at Pmom has been elucidated, little is known on the transactivation from lys, I and P promoters. Chapter III includes studies carried out to understand the process of activation at these promoters. Owing to the differences in their C-binding site and promoter architecture it was important to investigate the differential effect of C, if any at lys, I , P promoters compared to that at Pmom. Activators in prokaryotes are shown to stimulate different steps of transcription initiation pathway ranging from the polymerase binding to the promoters to the post recruitment steps of isomerization and promoter clearance. Effect of C at different steps of transcription initiation pathway was analysed. The results indicate that C is absolutely essential for transcription from lys, I and P promoters similar to mom. However, at these promoters C exerts its effect at the step of Isomerisation from closed complex to open complex formation. Thus, C acts at a single step here and the mode of activation is different from that observed at Pmom. C dimer binds DNA with high affinity and sequence specificity, to an interrupted palindromic sequence overlapping the -35 element of mom promoter. Mg2+ mediated conformational transitions in C protein are essential for its DNA binding and transactivation functions. Chapter IV deals with the identification of the Mg2+ coordinating residues in C protein. Primary sequence analyses lead to the identification of a putative metal coordinating motif (EXDXD) towards the N-terminus of the protein. These residues were subjected to site directed mutagenesis to infer their role in Mg2+ coordination, its associated allosteric transition required for specific interaction with DNA. Mutants showed an altered Mg2+ induced conformation, compromised DNA binding and reduced levels of transcription activation when compared to C protein. Though Mg2+ is widely used in various DNA transaction reactions, this study provides the first insights on the importance of metal-ion induced allosteric transitions in regulating transcription factor function.