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Bacterial-type DNA holliday junction resolvases in eukaryotic viruses
A D Garcia1, L Aravind, E V Koonin
1Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, and National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20892, USA.
Summary
Researchers identified a bacterial-like Holliday junction resolvase in poxviruses, crucial for DNA recombination. This enzyme, similar to bacterial RuvC, maintains genome integrity and promotes genetic diversity in viruses.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Homologous DNA recombination is vital for genetic diversity and genome stability.
- The Holliday junction (HJ) is a key intermediate in DNA recombination.
- No HJ-specific enzymes have been previously purified from metazoa or their viruses.
Purpose of the Study:
- To identify and characterize enzymes involved in Holliday junction resolution in viruses.
- To investigate the structural and functional similarities between viral and bacterial HJ resolvases.
Main Methods:
- Bioinformatic analysis of uncharacterized viral open reading frames.
- Expression and purification of the putative vaccinia virus resolvase (A22R protein).
- Biochemical assays to assess HJ binding and cleavage activity.
- Site-directed mutagenesis to investigate the role of conserved acidic amino acids.
Main Results:
- Identified bacterial RuvC-like HJ resolvase structural elements in poxviruses and iridoviruses.
- The recombinant vaccinia virus A22R protein specifically binds and cleaves synthetic HJs.
- Mutations in two conserved acidic amino acids abolished catalytic activity but not HJ binding.
Conclusions:
- Poxviruses encode a functional bacterial-type Holliday junction resolvase.
- This viral enzyme plays a role in DNA recombination, potentially impacting viral genome maintenance.
- The presence of such enzymes in metazoan viruses raises significant evolutionary questions regarding horizontal gene transfer.