Herpes Simplex Virus Ribonucleotide Reductase: Structural Features and Transcriptional Regulation

Nikas, Ioannis (1988) Herpes Simplex Virus Ribonucleotide Reductase: Structural Features and Transcriptional Regulation. PhD thesis, University of Glasgow.

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Ribonucleotide reductase (EC ) catalyses the direct reduction of all four ribonucleotides to the corresponding deoxyribonucleotides, this reaction being the first unique step in the de novo pathway of DNA biosynthesis. The herpes simplex virus type 1 (HSV-1)-induced enzyme is composed of two non-identical subunits, termed large (RR1) and small (RR2), which are dimers of the Vmw136 (RR1) and Vmw38 (RR2) polypeptides respectively. These polypeptides are specified by two early, unspliced and 3' co-terminal mRNAs with sizes of 5.0kb (RR1 mRNA) and 1.2kb (RR2 mRNA). The work presented in this thesis has been primarily directed at obtaining the predicted amino acid sequence of the HSV-1 RR1 polypeptide. The HSV-1 RR1 and RR2 amino acid sequences were analysed for conserved structural and functional features by comparisons to equivalent polypeptides of herpesviral and cellular origin. Other studies have identified the nucleotide changes in a portion of the RR1 gene of the HSV-1 temperature-sensitive (ts) mutant tsl207 and have examined the transcriptional regulation of RR1 and RR2 mRNA expression. The Nucleotide and Predicted Amino Acid Sequence of the HSV-1 RR1 Polypeptide. The nucleotide sequence of the HSV-1 DNA region encoding the RR1 polypeptide was obtained with the M13 dideoxy/chain termination method in combination with a 'shotgun' cloning approach. The sequencing data predicted that the RR1 DNA coding region is an open reading frame (ORF) of 3414 nucleotides which encodes a polypeptide of 1137 amino acids in length. In contrast to the remainder of the RR1 polypeptide, the N-terminal region contains unique amino acid composition features and seven sets of tandemly repeated amino acid sequences. A hypothetical scheme of evolutionary events leading to the formation of this region has been postulated. Further, as this region appears not be directly involved in enzymatic activity, a possible function has been suggested on the basis of two potential nuclear localisation signals. Amino Acid Conservation between Herpesvirus and Cellular Ribonucleotide Reductases. Analysis of amino acid conservation between the HSV-1 RR1 and RR2 polypeptides with identified or proposed large (RR L) and small (RRS) subunit polypeptides of herpesviral or cellular origin was performed using computer programs. a) Comparisons of the HSV-1 RR1 polypeptide with homologue RRL polypeptides. Comparison of the HSV-1 RR1 polypeptide with the equivalent herpes simplex virus type 2 (HSV-2) polypeptide revealed that they are essentially colinear with the exception of the N-terminal regions where number of insertions or deletions were predicted. Other analyses revealed that the RR1 N-terminal region was absent from other RRL polypeptides while the colinear parts exhibited clustered homology. b) Comparisons of the HSV-1 RR2 polypeptide with homologue herpesviral RRS polypeptides. Comparisons of the HSV-1 RR2 polypeptide with homologue herpesviral RRS polypeptides revealed the existence of clustered homology. The Escherichia coli (E. coli) tyrosine residue, on which the (essential for function) stable free radical has been localised, is conserved in all the RRS polypeptides examined These comparisons strongly indicate that the herpesviral RRL and RRS polypeptides examined are the constituents of the ribonucleotide reductase activities specified by these viruses. Conserved Structural and Potential Functional Features of the Herpesviral and Cellular Ribonucleotide Reductases. To identify more precisely regions of clustered homology and to determine potential functional features of the RRL and RRS polypeptide sequences, these were aligned with the consensus template alignment program and secondary structure predictions were obtained. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Virology
Date of Award: 1988
Depositing User: Enlighten Team
Unique ID: glathesis:1988-77752
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53
URI: https://theses.gla.ac.uk/id/eprint/77752

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