Thesis (Ph. D.)--University of Virginia, 1997. / Spine title: RNA packaging into HIV-1 Virions. Includes bibliographical references (152-174). Also available online through Digital Dissertations.

Reverse transcription in HIV-1 (human immunodeficiency virus type 1) is initiated from a tRNA, tRNALys3, that is annealed to the primer binding site (PBS) in the 5' region of viral RNA. This tRNA, along with the other major tRNALys isoacceptors, tRNALys1,2 , is selectively packaged into HIV-1 during its assembly. The formation of a tRNALys packaging/annealing complex is believed to involve the interaction between a Gag/GagPol/viral complex with a lysyl-tRNA synthetase (LysRS)/tRNALys complex, with Gag interacting specifically with LysRS, and GagPol interacting with both Gag and tRNALys. In fact, Gag particles alone will package LysRS, but GagPol, which binds tRNA Lys, is also required for incorporation of the tRNALys. / The model we propose for the tRNALys packaging/annealing complex predicts a possible interaction between LysRS and Pol sequences in GagPol, which might facilitate transfer of tRNALys3 from LysRS to the reverse transcriptase (RT) thumb domain where tRNALys3 binds. In this work, we demonstrate that, in addition to its interaction with Gag, LysRS also interacts with sequences within the connection/RNaseH domains in RT. Since these RT domains are not required for tRNALys packaging into HIV-1, the LysRS/Pol interaction is probably not involved in the transfer of tRNALys3 to RT. The LysRS/Pol interaction may instead be involved in tRNALys3 annealing since the connection domain in RT has been found to be required for this process. Also, since an interaction has been reported between Gag and Pol sequences in GagPol, we also investigated whether the Gag/LysRS/Pol interaction played an important role in stabilizing the Gag/Pol interaction, and found, using siRNA to LysRS, that it did not. / tRNALys3 annealing to viral RNA is promoted by nucleocapsid sequences in Gag and by mature NCp7, and we have examined the roles of Gag and NCp7 in this process. Gag- and NC-facilitated tRNALys3 annealing to HIV-1 RNA were measured both in vivo and in vitro, indirectly by the ability of annealed tRNALys3 to prime reverse transcription, and directly by measuring the occupancy of the PBS by tRNALys3. While tRNALys3 annealing can be carried out by both Gag and NCp7, exposure (in vivo or in vitro) of the tRNALys3/viral RNA complex to NCp7 is required for optimum placement of the tRNALys3. This is indicated by 1) tRNALys3's reduced ability to incorporate the first dNTP, dCTP, and 2) its more ready displacement from the PBS by DNA synthesized from a downstream primer. / It has been previously demonstrated that APOBEC3G (A3G) can inhibit tRNA Lys3 annealing to viral RNA, and we have used A3G to further dissect the roles of Gag and NCp7 in annealing, both in vitro and in vivo. Experiments studying how APOBEC3G (A3G) inhibits tRNA Lys3 annealing indicate that in protease-positive viruses, Gag-facilitated tRNALys3 annealing may only playa minor role. In vivo and in vitro, A3G only inhibits NCp7-facilitated annealing, and not Gag-facilitated annealing. Nevertheless, while Gag is able to show 70-80% of the annealing efficiency of NCp7 in a protease-negative virus, A3G can reduce annealing efficiency in protease-positive viruses to 40%. This appears to be due to the fact that, in vitro, the presence of NCp7 makes prior Gag-facilitated annealing susceptible to A3G. This suggests that in wild type viruses, any Gag-facilitated annealing of tRNALys3 to viral RNA that does occur is altered through an A3G-susceptible re-annealing by NCp7.

In the past three decades, various steps of the human immunodeficiency virus type 1 (HIV-1) life cycle have been thoroughly studied. Many of these steps, such as viral entry, reverse transcription and proteolysis have been targets of antiretroviral therapy. Retroviral genomic RNA (gRNA) dimerization appears essential for viral infectivity and this process appears to be chaperoned by the nucleocapsid (NC) protein of HIV-1. In this dissertation, the role of NC in genome dimerization and other aspects of the viral life cycle have been thoroughly studied. Various positions of the NC protein have been mutated through site-directed mutagenesis and relevant and dispensable positions of NC have been identified through this method. 34 of its 55 residues were mutated, individually or in small groups, in a panel of 40 HIV-1 mutants. It was found that the amino-terminus, the proximal zinc finger, the linker, and the distal zinc finger of NC each contributed roughly equally to efficient HIV-1 gRNA dimerization. The various mutations introduced into NC show the first evidence that gRNA dimerization can be inhibited by: 1) mutations in the N-terminus or the linker of retroviral NC; 2) mutations in the proximal or distal zinc finger of lentiviral NC; 3) mutations in the hydrophobic patch (plateau) or the conserved glycines of the proximal or the distal retroviral zinc finger. Some NC mutations impaired gRNA dimerization more than mutations inactivating the viral protease, indicating that gRNA dimerization may be stimulated by the NC component of the Gag polyprotein (Pr55gag). In the second section of my work, I studied the effect of Pr55gag processing on gRNA dimerization by introducing rate alternating mutants into Pr55gag protein cleavage sites. I showed that Maturation ofNCp15 into NCp9 is essential for fast rates of genomic RNA dimerization and maturation of NCp9 into NCp7 has no incidence on genomic RNA dimerization but is essential for viral replication. In order to delineate the amount of viral protease activity needed to produce mature virus 48 hours post transfection, we also studied, by cotransfection studies, the effect of various ratios of wild-type (BH10) and protease-inactive (PR- ) plasmids and found that HIV-1 reaches its full genomic RNA dimerization despite 75% unprocessed Pr55gag polyproteins. We have also shown that wild type BH10 plasmid can rescue those mutations in NCp7 protein that have an effect on gRNA dimerization through rescue experiments. Overall, this thesis sheds light on the role of NC in HIV-1 genome dimerization and other aspects of the viral life cycle and identifies the importance of each component of NC during these processes.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 89-108).

Made available in DSpace on 2015-11-11T12:13:55Z (GMT). No. of bitstreams: 2 allan_silva_ioc_dout_2014.pdf: 3186185 bytes, checksum: 31c3bfb195514d0e1800d36f02bb438f (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2015-04-14 / Fundação Oswaldo Cruz. Instituto Oswaldo Cruz. Rio de Janeiro, RJ, Brasil / Introdução e objetivos: Polimorfismos naturais de resistência aos agentes antivirais de atuação direta (DAAs) no vírus da hepatite C (HCV) podem representar um fator limitante para a eficácia dessa terapia. A análise de sequências virais de regiões geográficas distintas pode apresentar diferenças significativas nas frequências de mutações de resistência aos DAAs. Neste contexto, o objetivo deste estudo foi investigar as mutações associadas à resistência aos DAAs nos genes nãoestruturais (NS) do HCV em isolados virais que circulam no Brasil. Métodos: Foram estudados um total de 390 sequências do genótipo 1 do HCV de pacientes brasileiros virgens de tratamento cronicamente infectados. O RNA viral foi extraído, e as regiões abrangendo os genes NS3, NS4 e NS5 foram amplificadas por RT-PCR e sequenciadas. Resultados: No domínio NS3/4A protease, a variação V36L foi encontrada em 5,60% dos isolados do subtipo 1b, e a substituição T54S em 4,16% das sequências do subtipo 1a; na posição 55, 4,16% dos isolados continham a variação V55A, responsável por causar constrição no sítio de ligação do inibidor de protease boceprevir. Em relação à proteína NS4B, um isolado do subtipo 1b apresentou a substituição F98L, responsável por conferir resistência aos inibidores AP80978, PTC725 e silibina. Na proteína NS5A, 3,84% das sequências do subtipo 1a mostraram as mutações de resistência M28T ou Y93H, e 13,46%, as mutações secundárias H58P e E62D. Dentre os isolados do subtipo 1b, 3,70% continham a mutação Y93H, e 14,8%, as mutações secundárias R30Q, L31M, P58S e I280V Em NS5B, 25% das sequências do subtipo 1b brasileiras apresentaram a variação L159F na população viral dominante, mas nenhuma sequência do subtipo 1a exibiu tal substituição. Além disso, em 15 isolados do subtipo 1b (29%), foi observado o variante C316N, responsável por conferir resistência a inibidores não-nucleosídeos, enquanto que apenas 2,12% das sequências do isolado do subtipo 1a mostraram a substituição C316Y. A caracterização do subtipo 1a em clados 1 e 2 revelou que as sequências brasileiras das regiões NS3 e NS5A formaram um grupo distinto dentro do clado 1. Adicionalmente em NS3, esse clado apresentou uma característica fenotípica incomum em relação à presença de mutações de resistência aos inibidores macrocíclicos; em particular, a mutação Q80K foi encontrada na maioria das sequências de clado 1, mas não nas amostras brasileiras. Conclusões: Estes dados demonstram que as substituições de resistência a diferentes DAAs podem ser encontradas em isolados circulando no Brasil em pacientes virgens de tratamento antiviral. Além disso, os isolados brasileiros do HCV apresentam um padrão distinto de diversidade genética, reforçando a importância destas informações em futuras abordagens terapêuticas / Natural resistance polymorphisms to direct antivi ral agents (DAAs) in hepatitis C virus (HCV) may represent a limiting factor for therapy efficacy. Analysis of viral sequences from distinct geographical regions may sh ow significant differences in the frequencies of resistance mutations to DAAs. In this context, the aim of this study was to investigate mutations associated with resistance to DAAs of HCV non-struc tural genes (NS) in viral isolates circulating in Brazil. Methods : A total of 390 HCV genotype 1 sequences from ther apy-naive Brazilian patients chronically infected. Viral RNA was extracted, and the region encompassing the non-structural genes NS3, NS4, and NS5 was RT-PCR amplified and se quenced. Results : In the NS3/4A protease domain, a V36L variation was found in 5,60% of subt ype 1b isolates and a T54S substitution in 4,16% of subtype 1a sequences; at position 55, 4,16 % of strains contained the V55A variation which is responsible to cause constriction in the b inding site of the protease inhibitor boceprevir. Concerning the NS4B protein, one subtype 1b isolate showed the F98L substitution, responsible for conferring resistance to inhibitors AP80978, PTC725 and Silybin. In the NS5A protein, 3,84% of subtype 1a sequences showed the resistance mutation s M28T and Y93H, while 13,46%, the secondary mutations H58P and E62D. Among subtype 1b isolates, 3,70% of patients showed the Y93H mutation, while 14,8% the secondary mutations R30Q, L31M, P58S and I280V. For NS5B, 25% of Brazilian subtype 1b sequences presented the L159F variation in the dominant viral population, but none of subtype 1a sequence showed such substitution. Moreover, 15 subtype 1b isolates (29%), were observed the C316N variant, re sponsible to confer resistance to non-nucleoside inhibitors, while only 2,12% of subtype 1a isolates showed the C316Y substitution. Characterization of subtype 1a in clades 1 and 2 re vealed that Brazilian sequences of NS3 and NS5A regions formed a distinct group inside clade 1 . Additionally to NS3, this clade presented an unusual phenotypic characteristic in relation to th e presence of resistance mutations to macrocyclic inhibitors; in particular, the mutation Q80K was fo und in the majority of clade 1 sequences, but not in the Brazilian isolates. Conclusions : These data demonstrate that substitutions conferr ing resistance to different DAAs can be found in isolat es circulating in Brazil in treatment-naive patients. Moreover, Brazilian HCV isolates display a distinct pattern of genetic diversity, reinforcing the importance of this informations in future therapeutic approaches.

No description available.

No description available.

Human immunodeficiency virus (HIV) is the causing agent of the acquired immune deficiency syndrome (AIDS). Like all retroviruses, HIV carries two copies of viral genomic RNA in each virion. HIV genome encodes three structural genes, including gag, pol and env, as well as two regulatory genes (rev and tat) and four accessory genes (vif, vpr, vpu and nef). It is noted that none of these nine viral proteins bears the helicase activity. Helicases are able to unwind RNA duplex and remodel the structure of RNA-protein (RNP) complexes using energy derived from hydrolysis of nucleotide triphosphates (NTPs). They are involved in every step of cellular RNA metabolisms. It is conceivable that HIV needs to exploit cellular RNA helicases to promote the replication of its RNA at various steps such as transcription, folding and transport. / In this study, we found that a DEAD-box protein named DDX24 associates with HIV-1 Gag in an RNA-dependent manner but is not found within virus particles. Knockdown of DDX24 inhibits the packaging of HIV-1 RNA and thus diminishes viral infectivity. The decreased viral RNA packaging as a result of DDX24-knockdown is observed only in the context of the Rev/RRE (Rev response element)-dependent but not the CTE (constitutive transport element)-mediated nuclear export of viral RNA, which is explained by the specific interaction of DDX24 with the Rev protein. We propose that DDX24 acts at the early phase of HIV-1 RNA metabolism prior to nuclear export and the consequence of this action extends to the viral RNA packaging stage during virus assembly.

Human Immunodeficiency Virus type I genome consists of two identical RNA molecules that are non-covalently linked to form a dimer. HIV-1 immature and mature genomic RNA (gRNA) dimers were found in protease defective (PR -) and wild type virions, respectively, and the 5'untranslated region (5' UTR) was shown to play key roles during the genome dimerization process; but the dimerization mechanism still remains to be clarified My research project is to characterize the dimerization process and the role of 5' UTR in genome dimerization in virions produced by tissue culture cells. I'll firstly show the dimer maturation processes of HIV-1 gRNA isolated from newly released to grown-up (≥10h old) wild type, PR-, and SL1 defective (DeltaIDS) virions respectively. The results showed that HIV-1 gRNA dimer maturation process was protease-dependent and involved multiple steps: from low to high dimerization level and dimer thermostability, and from low dimer mobility to intermediate and high mobility. PR- virions did not freeze gRNA conformation in the primordial nascent state and gRNA changed from monomeric in newly released virions to half dimeric in grown-up virions, which showed that genome was packaged in the form of monomeric RNA or fragile dimers, more thermolabile than immature dimers in grown-up PR- virions. DeltaDIS inhibited gRNA dimerization by about 50% in newly released virions, though grown-up DeltaDIS gRNA was fully dimeric, which indicated that the DIS played the initiation role in gRNA dimerization in HIV-1 virions. The gRNA dimerization rate in PR- or DeltaDIS virions was much slower than that in wild type virions. These results show for the first time the whole process of dimer maturation after virion release, the gRNA conformation rearrangement in PR- virions, and the initiation role of the DIS in HIV-1 virions. Next, I'll provide a rather systematic search for the contribution of different regions in 5' UTR to HIV-1 gRNA dimerization by studying selected mutations singly or together with defective SL1. The results showed that the 5'trans-activation response element (5'TAR) was directly involved in gRNA dimerization, and a long distance base-pairing interaction between a sequence in U5 region (nts105-1l5) and another around the initiation codon of the gag gene (nts334-344) was structurally contributive to gRNA dimerization. Deletions of sequences around the 3'end of Primer Binding Site (PBS) stem-loop moderately decreased gRNA dimerization level. Other sequences in 5' UTR except DIS/SL1, which was previously known to play important roles, didn't show any systematic role. Here the results suggested that the absence of inhibition on gRNA dimerization level with defective DIS might be the compensation of the direct role of 5'TAR; and wild type-like dimerization level of DeltaTAR must be the direct contribution of the DIS.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.