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Publication Abstract from PubMed

Packaging of viral genomes into preformed procapsids requires the controlled and synchronized activity of an ATPase and a genome-processing nuclease, both located in the large (L) terminase subunit. In this paper, we have characterized the structure and regulation of bacteriophage P22 L-terminase (gp2). Limited proteolysis reveals a bipartite organization, consisting of an N-terminal ATPase core flexibly connected to a C-terminal nuclease domain. The 2.02 A crystal structure of P22 headful nuclease obtained by in drop proteolysis of full length L-terminase (FL-L-terminase) reveals a central seven-stranded beta-sheet core that harbors two magnesium ions. Modeling studies with DNA suggest the two ions are poised for two-metal ion-dependent catalysis, but the nuclease DNA-binding surface is sterically hindered by a loop-helix (L1-alpha2) motif, which is incompatible with catalysis. Accordingly, the isolated nuclease is completely inactive in vitro, while it exhibits endonucleolytic activity in the context of FL-L-terminase. Deleting the auto-inhibitory L1-alpha2 motif (or just the loop L1) restores nuclease activity to a level comparable to FL-L-terminase. Together, these results suggest that the activity of P22 headful nuclease is regulated by an intramolecular cross-talk with the N-terminal ATPase domain. This cross-talk allows for precise and controlled cleavage of DNA that is essential for genome-packaging.

Structure of p22 headful packaging nuclease.,Roy A, Cingolani G J Biol Chem. 2012 Jun 19. PMID:22715098^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.