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Structure. 2012 Aug 8;20(8):1403-13. doi: 10.1016/j.str.2012.05.014. Epub 2012 Jul 5.

Small terminase couples viral DNA binding to genome-packaging ATPase activity.

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1
Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 233 South 10th Street, Philadelphia, PA 19107, USA.

Abstract

Packaging of viral genomes into empty procapsids is powered by a large DNA-packaging motor. In most viruses, this machine is composed of a large (L) and a small (S) terminase subunit complexed with a dodecamer of portal protein. Here we describe the 1.75 Å crystal structure of the bacteriophage P22 S-terminase in a nonameric conformation. The structure presents a central channel ∼23 Å in diameter, sufficiently large to accommodate hydrated B-DNA. The last 23 residues of S-terminase are essential for binding to DNA and assembly to L-terminase. Upon binding to its own DNA, S-terminase functions as a specific activator of L-terminase ATPase activity. The DNA-dependent stimulation of ATPase activity thus rationalizes the exclusive specificity of genome-packaging motors for viral DNA in the crowd of host DNA, ensuring fidelity of packaging and avoiding wasteful ATP hydrolysis. This posits a model for DNA-dependent activation of genome-packaging motors of general interest in virology.

PMID:
22771211
PMCID:
PMC3563279
DOI:
10.1016/j.str.2012.05.014
[Indexed for MEDLINE]
Free PMC Article
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