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Diss. (sammanfattning) Umeå : Univ., 2004. / Härtill 4 uppsatser.

Non-ribosomally synthesised natural products derived mainly from bacteria and fungi act as important therapeutic agents. Due to their complex structures it is difficult to chemically synthesise such compounds, therefore the engineering of biosynthetic and biocatalytic pathways that are vital for their production are the aims of this thesis. The first project involved the study of the biosynthesis of 3-O-methyl aspartic acid (OmAsp) in the antibiotic A54145. We demonstrated that LptL functions as an asparagine hydroxylase. We also predicted that LptJ and LptK are involved in the biosynthesis of OmAsp, although we did not find evidence of this non-standard amino acid in the antibiotic CDA when we over-expressed both proteins in Streptomyces coelicolor. The second project involved the study of the chlorination and mannosylation of hydroxyphenyl glycine (Hpg) residues in ramoplanin. We over-expressed the putative chlorinase and mannosyl transferase separately in the enduracidin-producer, in which the production of enduracidin has been characterised. We then found that trichlorinated and mannosylated enduracidin analogues were produced. The final project involved the re-engineering of a preQ1 riboswitch. We successfully created ten preQ1 riboswitch mutants fused to the reporter gene lacZ in Bacillus subtilis, all of which showed different levels of β-galactosidase activity. Subsequently, we found that the preQ1 C17U mutant riboswitch can respond specifically to the synthetic ligands 5-(aminomethyl)furo[2,3-d]pyrimidine-2,4-diamine (D6) and 2,4-diamino-7H-pyrrolo[2,3-d]pyrimidine-5-carbonitrile (D9) to control gene expression in a dose dependent manner. The results described here show the successful production of variant antibiotics by bio-engineering and the use of an engineered preQ1 riboswitch as a tool for regulating gene expression.

Ribosomes which conduct protein synthesis in all living organisms are comprised of two subunits. The large 60S ribosomal subunit catalyzes peptidyl transferase reactions and includes the polypeptide exit tunnel, while the small (40S) ribosomal subunit recruits incoming messenger RNAs (mRNAs) and performs proofreading. The plant 80S cytoplasmic ribosome is composed of 4 ribosomal RNAs (rRNAs: 25-28S, 5.8S and 5S in the large subunit and 18S in the small subunit) and 81 ribosomal proteins (r-proteins: 48 in the large subunit, 33 in the small subunit). RPS15a, a putative small subunit primary binder, is encoded by a six member gene family (RPS15aA-F), where RPS15aB and RPS15aE are evolutionarily distinct and thought to be incorporated into mitochondrial ribosomes. In vitro synthesized cytoplasmic 18S rRNA, 18S rRNA loop fragments, and RPS15a mRNA molecules were combined in electrophoretic shift assays (EMSAs) to determine the RNA binding characteristics of RPS15aA/-D/-E/-F. RPS15aA/F, -D and -E bind to cytoplasmic 18S rRNA in the absence of cellular components. However, RPS15aE r-protein tested that binds mitochondrial 18S rRNA. In addition, RPS15aA/F only binds one of three 18S rRNA loop fragments of helix 23 whereas RPS15aD/-E bind all three 18S rRNA helix 23 loop fragments. Additionally, RPS15aD and RPS15aE did not bind their respective mRNA transcripts, likely indicating that this form of negative feedback is not a post-transcriptional control mechanism for this r-protein gene family. Furthermore, the addition of RPS15a transcripts to the EMSAs did not affect the binding of RPS15aA/F, -D and -E to 18S rRNA helix 23 loop 4-6, indicating that rRNA binding is specific. Supershift EMSAs further confirmed the specificity of RPS15aA/F and RPS15aE binding to loop fragment (4-6) of 18S rRNA. Taken together, these data support a role for RPS15a in early ribosome small subunit assembly.

Ribosomes which conduct protein synthesis in all living organisms are comprised of two subunits. The large 60S ribosomal subunit catalyzes peptidyl transferase reactions and includes the polypeptide exit tunnel, while the small (40S) ribosomal subunit recruits incoming messenger RNAs (mRNAs) and performs proofreading. The plant 80S cytoplasmic ribosome is composed of 4 ribosomal RNAs (rRNAs: 25-28S, 5.8S and 5S in the large subunit and 18S in the small subunit) and 81 ribosomal proteins (r-proteins: 48 in the large subunit, 33 in the small subunit). RPS15a, a putative small subunit primary binder, is encoded by a six member gene family (RPS15aA-F), where RPS15aB and RPS15aE are evolutionarily distinct and thought to be incorporated into mitochondrial ribosomes. In vitro synthesized cytoplasmic 18S rRNA, 18S rRNA loop fragments, and RPS15a mRNA molecules were combined in electrophoretic shift assays (EMSAs) to determine the RNA binding characteristics of RPS15aA/-D/-E/-F. RPS15aA/F, -D and -E bind to cytoplasmic 18S rRNA in the absence of cellular components. However, RPS15aE r-protein tested that binds mitochondrial 18S rRNA. In addition, RPS15aA/F only binds one of three 18S rRNA loop fragments of helix 23 whereas RPS15aD/-E bind all three 18S rRNA helix 23 loop fragments. Additionally, RPS15aD and RPS15aE did not bind their respective mRNA transcripts, likely indicating that this form of negative feedback is not a post-transcriptional control mechanism for this r-protein gene family. Furthermore, the addition of RPS15a transcripts to the EMSAs did not affect the binding of RPS15aA/F, -D and -E to 18S rRNA helix 23 loop 4-6, indicating that rRNA binding is specific. Supershift EMSAs further confirmed the specificity of RPS15aA/F and RPS15aE binding to loop fragment (4-6) of 18S rRNA. Taken together, these data support a role for RPS15a in early ribosome small subunit assembly.

Eukaryotic ribosome synthesis is a complex process that consumes a lot of energy and involves several hundreds of trans-acting factors that transiently associate with nascent ribosomes. Biogenesis of ribosomal subunits (the small 40S and the large 60S) starts with transcription of a long precursor ribosomal RNA (pre-rRNA) by RNA polymerase I (Pol I) in the nucleolus. This is a key step that globally controls yeast ribosome synthesis. The pre-rRNA, ‘the 35S transcript’, encodes the mature sequence (18S, 5.8S, and 25S) rRNA constituents of both the 40S and 60S subunits. The 35S transcript is subsequently modified, cleaved (processed) and assembled with numerous structural ribosomal proteins and ribosome synthesis factors (trans-acting factors) to form various ribosomal particles (pre-ribosomes, precursors to the 40S and 60S subunits) along ribosome assembly pathway. In the budding yeast Saccharomyces cerevisiae, it has been reported recently that the processing of the 35S nascent transcript and the assembly of pre-ribosomes occur concomitantly with Pol I transcription in the nucleolus. In this process, the growing Pol I transcript gradually assembles with pre-40S structural ribosomal proteins and ribosomal synthesis factors to form the so-called ‘SSU-processome’ or ‘90S pre-ribosome’, the earliest precursor of the 40S subunit. The SSU-processome/90S pre-ribosome localizes to the nucleolus and consists of the 35S pre-rRNA, the U3 small nucleolar (sno) RNA, about a dozen of 40S ribosomal proteins and more than forty ribosome synthesis factors. The U3 snoRNA and pre-40S ribosome synthesis factors are all implicated in the processing of the 35S precursor (at sites A0, A1 and A2) and therefore in the synthesis of the 18S rRNA component of the 40S subunit. Significantly, the association of the U3 snoRNA with the growing 35S transcript is important for pre-40S assembly, whereas its dissociation from the processed transcript (following cleavage at sites A0-A2) is crucial for the overall structural remodeling of the 18S rRNA and for the formation of pre-40S ribosomes from the earliest precursor 90S particles. This thesis mostly addresses the identification and functional characterization of Esf2 and Bfr2, two novel 40S synthesis factors, components of the SSU-processome/90S pre-ribosome in yeast. Both proteins localize to the nucleolus and their genetic depletions lead to failure in the production of 40S subunits. In the absence of either factor, the 35S pre-rRNA is not processed at sites A0-A2 and the 18S rRNA is not synthesized. Also, pre-ribosome assembly is affected and pre-40S ribosomes fail to mature properly. Strikingly, in the absence of either factor, the U3 snoRNA remains associated with unprocessed 35S transcript within pre-ribosomes indicating that Esf2 and Bfr2 are required to dissociate U3 from pre-ribosomes. This process also involves RNP (ribonucleoprotein particle) unwinding activities of the putative RNA helicase Dbp8. La biogenèse du ribosome eucaryote est un processus complexe qui consomme beaucoup d’énergie et implique plusieurs centaines de facteurs trans qui s’associent de manière transitoire avec les pré-ribosomes en cours de formation. La biogenèse des sous-unités ribosomiques (la petite sous-unité 40S et la grande sous-unité 60S) débute dans le nucléole par la synthèse d’un long précurseur d’ARN ribosomique (le pré-ARNr, dit 35S chez la levure Saccharomyces cerevisiae) par l’ARN Polymérase I (Pol I). Ceci constitue une étape clé dans le contrôle global de la synthèse du ribosome chez la levure. Le pré-ARNr 35S renferme les séquences des ARNr matures 18S (ARNr de la sous-unité 40S) et 5.8S et 25S (deux des trois ARNr de la sous-unité 60S). Le pré-ARNr 35S subit un long processus de maturation et d’assemblage au cours duquel il est modifié, clivé (on parle du « processing » du pré-ARNr) et s’assemble avec des protéines ribosomiques (« RP », composants structuraux des sous-unités ribosomiques matures) et de nombreux facteurs de synthèse (facteurs trans) pour former différentes particules pré-ribosomiques (précurseurs des sous-unités 40S et 60S). Chez la levure S. cerevisiae, il a récemment été montré que le processing du pré-ARNr 35S et l’assemblage des pré-ribosomes se produisent de manière concomminante avec la transcription Pol I dans le nucléole. Ainsi, le transcrit Pol I en cours de synthèse s’assemble progressivement avec des facteurs de synthèse ainsi que des RP pour former le « SSU processome » ou « pré-ribosome 90S », tout premier précurseur de la petite sous-unité 40S. Le SSU processome/pré-ribosome 90S est localisé dans le nucléole et est consisté du pré-ARNr 35S naissant, du petit ARN nucléolaire (snoRNA) U3, d’une douzaine de RP de la petite sous-unité 40S et de plus de 40 facteurs de synthèse. Le snoRNA U3 et ces facteurs de synthèse sont tous impliqués dans les clivages du pré-ARNr 35S aux sites A0, A1 et A2, et donc dans la biogenèse de l’ARNr 18S. L’association du snoRNA U3 avec le pré-ARNr 35S naissant est importante pour l’assemblage du SSU processome/pré-ribosome 90S. Par ailleurs, sa dissociation après les clivages aux sites A0-A2 permet un remodelage structural général de l’ARNr 18S et la formation du « pré-ribosome 40S » à partir de la particule précoce 90S. Au cours de cette thèse, nous avons identifié et caractérisé fonctionnelement chez la levure deux nouveaux facteurs de synthèse de la petite sous-unité 40S et composants du SSU processome/pré-ribosome 90S: Esf2 et Bfr2. Ces deux protéines sont localisées dans le nucléole. Leur déplétion entraîne une incapacité à produire la sous-unité ribosomique 40S. En l’absence d’Esf2 ou Bfr2, le pré-ARNr 35S n’est plus clivé aux sites A0-A2 et l’ARNr 18S mature n’est plus produit. L’assemblage des pré-ribosomes est aussi affecté, notamment la formation du pré-ribosome 40S. De manière importante, en l’absence de l’un ou l’autre de ces facteurs, le snoRNA U3 reste associé au pré-ARNr 35S non clivé au sein des pré-ribosomes, indiquant qu’Esf2 et Bfr2 sont requises pour la dissociation d’U3 des pré-ribosomes. Ce processus implique aussi Dbp8, une hélicase à ARN présumée.

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"July 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 166-177) / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Chiu, Yu Hin Teddy. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 118-129). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract --- p.ii / Table of Content --- p.vi / Abbreviations --- p.x / Naming system for mutant proteins --- p.xi / Abbreviation for amino acid --- p.xii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- What are acidic ribosomal proteins? --- p.1 / Chapter 1.2 --- Why P-proteins are so important? --- p.13 / Chapter 1.3 --- Research objectives --- p.15 / Chapter Chapter 2 --- Materials and Methods --- p.17 / Chapter 2.1 --- List of buffers and media --- p.17 / Chapter 2.1.1 --- Preparation of buffers and media --- p.17 / Chapter 2.1.2 --- Buffers for preparing competent cells --- p.17 / Chapter 2.1.3 --- Media for bacterial culture --- p.17 / Chapter 2.1.4 --- Buffers for nucleic acid electrophoresis --- p.19 / Chapter 2.1.5 --- Buffers for protein electrophoresis --- p.19 / Chapter 2.1.6 --- Buffers for interaction studies using BIAcore 3000 --- p.21 / Chapter 2.2 --- General methods --- p.23 / Chapter 2.2.1 --- Preparation of Escherichia coli (E.coli.) competent cells --- p.23 / Chapter 2.2.2 --- Transformation of Escherichia coli (E.coli.) competent cells --- p.23 / Chapter 2.2.3 --- DNA cloning --- p.24 / Chapter 2.2.3.1 --- DNA cloning by polymerase chain reaction (PCR) --- p.24 / Chapter 2.2.3.2 --- Agarose gel electrophoresis of DNA --- p.25 / Chapter 2.2.3.3 --- Extraction and purification of DNA from agarose gels --- p.25 / Chapter 2.2.3.4 --- Restriction digestion of DNA --- p.25 / Chapter 2.2.3.5 --- Ligation of digested insert and expression vector --- p.27 / Chapter 2.2.3.6 --- Verification of insert by PCR --- p.27 / Chapter 2.2.3.7 --- Mini-preparation of plasmid DNA --- p.28 / Chapter 2.2.4 --- Polyacrylamide gel electrophoresis (PAGE) of protein --- p.29 / Chapter 2.2.4.1 --- SDS-polyacrylamide gel electrophoresis (SDS-PAGE) --- p.29 / Chapter 2.2.4.2 --- Tricine SDS-polyacrylamide gel electrophoresis --- p.30 / Chapter 2.2.4.3 --- Native polyacrylamide gel electrophoresis --- p.31 / Chapter 2.2.4.4 --- Commassie brilliant blue staining of proteinin polyacrylamide gel --- p.32 / Chapter 2.2.4.5 --- Zinc Imidazole staining of protein in polyacrylamide gel --- p.33 / Chapter 2.2.5 --- Protein concentration determination --- p.33 / Chapter 2.2.6 --- Expression of recombinant proteins --- p.33 / Chapter 2.2.6.1 --- Expression of recombinant proteins using LB --- p.33 / Chapter 2.2.6.2 --- Expression of recombinant proteins using minimal medium --- p.34 / Chapter 2.2.6.3 --- Harvest and lysis of bacterial cell culture --- p.34 / Chapter 2.3 --- Protein purification --- p.36 / Chapter 2.3.1 --- Purification of ribosomal protein P1 and its deletion mutants --- p.36 / Chapter 2.3.1.1 --- Purification of P1 --- p.36 / Chapter 2.3.1.2 --- Purification of P1ΔC25 --- p.36 / Chapter 2.3.1.3 --- Purification of HisMBP-P1ΔC40 and HisMBP-P1ΔC47 --- p.37 / Chapter 2.3.2 --- Purification of ribosomal protein P2 and its deletion mutants --- p.38 / Chapter 2.3.2.1 --- Purification of P2 --- p.38 / Chapter 2.3.2.2 --- Purification of P2ΔC46 and P2ΔC55 --- p.39 / Chapter 2.4 --- "Preparation and purification of protein complexes formed by P1, P2 and their truncation mutants" --- p.40 / Chapter 2.4.1 --- Preparation of complexes by Co-refolding in urea buffer --- p.40 / Chapter 2.4.1.1 --- Preparation of P1 or P1ΔC25 involved complexes --- p.40 / Chapter 2.4.1.2 --- Preparation of P1ΔC40/ P2ΔC46 and P1ΔC47/ P2ΔC46 --- p.41 / Chapter 2.4.2 --- Preparation of complexes by direct mixing --- p.42 / Chapter 2.5 --- Laser light scattering for the determination of molecular weight of protein and their complexes --- p.43 / Chapter 2.5.1 --- Chromatography mode light scattering experiment (SEC/LS) --- p.43 / Chapter 2.6 --- Interaction study of P1 and P2 using BIAcore 3000 surface plasmon resonance (SPR) biosensor --- p.45 / Chapter 2.6.1 --- Immobilization of P2 onto CM5 sensor chips --- p.45 / Chapter 2.6.2 --- Kinetic measurements of P1 and P2 interaction --- p.46 / Chapter Chapter 3 --- Determination of domain boundaries for dimerization of P1/P2 --- p.46 / Chapter 3.1 --- Introduction --- p.48 / Chapter 3.2 --- Preparation of P1，P2 and their truncation mutants --- p.50 / Chapter 3.2.1 --- Construction of P1 and P2 N-terminal domains (NTDs) --- p.50 / Chapter 3.2.2 --- P1 and its truncation mutants were purified in denaturing condition --- p.53 / Chapter 3.2.3 --- "P2, P2AC46 and P2AC55 were purified" --- p.56 / Chapter 3.3 --- Formation of complexes from P1，P2 and their truncation mutants --- p.59 / Chapter 3.3.1 --- "P1, P2 and their truncation mutants interact to yield protein complexes" --- p.49 / Chapter 3.3.2 --- P1AC47/P2AC46 is the smallest N-terminal domain complex --- p.63 / Chapter 3.4 --- Perturbation of P2 NTD upon binding with P1 --- p.65 / Chapter 3.4.1 --- "1H, 15N 一 HSQC spectrum of P2AC46 changed significantly upon binding with P1" --- p.65 / Chapter 3.4.2 --- P1/P2AC46 prepared by co-refolding and direct mixing give the same HSQC spectra --- p.66 / Chapter 3.5 --- Discussion --- p.69 / Chapter Chapter 4 --- Stochiometry of P1/P2 Complex is revealed by Light scattering --- p.72 / Chapter 4.1 --- Introduction --- p.72 / Chapter 4.2 --- P1 and P2 interact in 1:1 molar ratio --- p.77 / Chapter 4.2.1 --- Purified P2 exists as homo-dimer in solution --- p.77 / Chapter 4.2.2 --- The stochiometry of P1/P2 complex is 1:1 --- p.78 / Chapter 4.3 --- Stochiometries of P1 and P2 truncation mutant complexes varied from the full-length counterparts --- p.81 / Chapter 4.3.1 --- P2AC46 and P2AC55 exist as homo-dimer in solution --- p.81 / Chapter 4.3.2 --- "P1/P2AC46, P1AC25/P2 and P1AC40/P2AC46 retain the hetero-dimeric stochiometry of 1:1" --- p.82 / Chapter 4.3.3 --- P2AC55 involved complexes show a different stochiometry --- p.83 / Chapter 4.4 --- Discussion --- p.87 / Chapter Chapter 5 --- Binding kinetics of P1/P2 complex studied by surface plasmon resonance --- p.92 / Chapter 5.1 --- Introduction --- p.92 / Chapter 5.2 --- Kinetic parameters of P1 and P2 interaction is revealed by surface plasmon resonance --- p.95 / Chapter 5.2.1 --- P2 was coupled to CM5 sensor chip surface for kinetic studies --- p.95 / Chapter 5.2.2 --- Reduction of basal response after the 1st binding of P1 --- p.96 / Chapter 5.2.3 --- P1 induced a great change in response unit than P2 upon binding with immobilized P2 --- p.99 / Chapter 5.2.4 --- Kinetic parameters of P1 and P2 interaction was studied by introducing P1 to the sensor chip surface --- p.101 / Chapter 5.2.5 --- Dissociation constant derived from 1:1 Langmuir binding isotherm --- p.102 / Chapter 5.2.6 --- Dissociation constant derived from responses at equilibrium (Req) --- p.103 / Chapter 5.3 --- Discussion --- p.106 / Chapter Chapter 6 --- Conclusion and discussion of the study --- p.112 / References --- p.118 / Appendix --- p.130