The B/C gene of simian virus 40

Abstract

Temperature-sensitive B, C, and BC mutants of Simian virus 40 (SV40) map in the late region of the viral genome in Hin fragments K, F, J, and G, a DNA segment of about 1200 nucleotide pairs ( Lai, C.-J., and Nathans, D. (1975) Virology 66, 70–81). To define the B/C region further, mutants of SV40 with deletions in this genomic segment were constructed by enzymatic excision of DNA from the viral genome, followed by cloning in the presence of a complementing tsA mutant of SV40. After localization of deleted genome segments by analysis of endo R fragments and electron microscopic heteroduplex mapping, selected deletion mutants were tested for complementation by ts mutants and were screened for their ability to produce new viral proteins in infected cells. Complementation tests indicated that B/C deletion mutations are in a cistron distinct from that of tsA and tsD mutations and that the junction between the B/C and D genes is within Hin-K. Two of the deletion mutants produced new proteins detectable in infected cells. More detailed analysis of one of these proteins (of molecular weight 25,000) indicated that it precipitated with antiserum against dissociated SV40 capsids, and that all but one of its lysine-containing tryptic peptides cochromatographed with SV40 VP1 tryptic peptides. We conclude that the B/C gene, containing approximately 1200 nucleotide pairs, codes for VPl. Since deletion mutants lacking Hin-E do not complement B mutants, we suggest that the Hin-E DNA segment has a signal required for expression of the B/C gene.