Molecular Biology

Circle of One

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Science  15 Sep 2006:
Vol. 313, Issue 5793, pp. 1542-1543
DOI: 10.1126/science.313.5793.1542d

All living things must maintain and repair their genomes, and nonhomologous end joining (NHEJ) is one of the most important pathways for patching up potentially disastrous double-strand (ds) breaks in DNA; so-called Ku proteins play a central role in the process. But viruses, so it was thought, don't seem to use NHEJ in this way. Corndog and Omega are dsDNA viruses or, more precisely, bacteriophages that infect bacteria, in this case, Mycobacterium species. Oddly enough, as Pitcher et al. now show, Corndog and Omega both contain Ku homologs in their genomes. The viral Ku proteins can work together with the bacterial ligase LigD to repair ds breaks in a yeast system. This suggests that NHEJ is somehow involved in the viral life cycle, where previously there was no indication of such a requirement.

Corndog and Omega enter bacterial cells as linear viruses that must circularize to allow rolling circle replication-an essential part of the viral life cycle. Related viruses, such as Lambda, have long 9-nucleotide (nt) cohesive (cos) ends that provide a favorable equilibrium for self-association. Corndog and Omega have very short cos ends, of only 4 nt, which are too short to self-associate efficiently and promote genome circularization. Thus the viral Ku, working together with the host LigD, may help to bring the cos ends together, paralleling their function in dsDNA break repair. — GR

Mol. Cell 23, 743 (2006).

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