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FOR THE RECORD

A structural rationale for SV40 Vp1 temperature-sensitive mutants and their complementation

¹ Molecular Biology Institute and Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California 90095, USA
² X-Ray Diffraction Facility, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
³ Department of Microbiology and Immunology, Penn State College of Medicine, Hershey, Pennsylvania 17033, USA
⁴ Infectious and Inflammatory Disease Center, The Burnham Institute for Medical Research, La Jolla, California 92037, USA

(RECEIVED March 7, 2006; FINAL REVISION May 26, 2006; ACCEPTED May 28, 2006)

Two groups of temperature-sensitive (ts) mutants, termed ts B and ts C, have mutations in the major capsid protein of SV40, Vp1. These mutants have virion assembly defects at the nonpermissive temperature, but can complement one another when two mutants, one from each group, coinfect a cell. A third group of mutants, termed ts BC, have related phenotypes, but do not complement other mutants. We found that the mutations fall into two structural and functional classes. All ts C and one ts BC mutations map to the region close to the Ca²⁺ binding sites, and are predicted to disrupt the insertion of the distal part of the C-terminal invading arm (C-arm) into the receiving clamp. They share a severe defect in assembly at the nonpermissive temperature, with few capsid proteins attached to the viral minichromosome. By contrast, all ts B and most ts BC mutations map to a contiguous region including acceptor sites for the proximal part of the C-arm and intrapentamer contacts. These mutants form assembly intermediates that carry substantial capsid proteins on the minichromosome. Thus, accurate virion assembly is prevented by mutations that disrupt interactions between the receiving pentamer and both the proximal and distal parts of the C-arms, with the latter having a greater effect. The distinct spatial localization and assembly defects of the two classes of mutants provide a rationale for their intracistronic complementation and suggest models of capsid assembly.

Keywords: viral assembly; complementation; temperature-sensitive mutants; SV40; capsid

Article published online ahead of print. Article and publication date are at http://www.proteinscience.org/cgi/doi/10.1110/ps.062195606.

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