Simian Virus 40 Assembly, Studied by Temperature-Induced Conformational Changes in Capsid Protein VP1

Analysis of temperature-sensitive mutations in the simian virus 40 gene encoding virion protein 1

Temperature-sensitive (ts) assembly mutants of the tumorigenic virus simian virus 40 (SV40) fail to follow the normal pathway of virion morphogenesis at 40 degrees C. The mutations were previously mapped to the gene coding for the major virion protein VP1 and fall into three groups: tsB, tsBC, and tsC. We have determined the tsB/C mutations by DNA sequence analysis and deduced the corresponding amino acid substitutions. We find that the mutations are global and span 68% of the VP1 gene. They result predominantly in single amino acid substitutions. The B mutations are localized between nucleotides 1667 and 2091, spanning the VP1 amino acid residues 54-195. With the exception of one mutation in tsC260, the C group mutations occur between the nucleotides 2141 and 2262, spanning VP1 residues 212-252. The tsBC substitutions are not localized within a distinct region. We present a model for the VP1 structure. The model correlates the distribution of ts assembly mutations in the SV40 VP1 gene with the VP1 functional domains, deduced form the phenotypes exhibited by the assembly mutants, and the VP1 structural domains, deduced recently from the cryoelectron microscopic studies of the SV40 virions. We summarize the behavior of the SV40 ts mutants and discuss the possible relationship between the ts phenotype and amino acid substitutions.