FUNCTIONAL-CHARACTERIZATION OF THE EARLY AND LATE MESSENGER-RNAS OF SIMIAN-VIRUS-40

We have characterized the early SV40 mRNAs by size fractionation on acrylamide gels followed by in vitro translation and immunoprecipitation. The mRNA for the 17K T antigen migrates more slowly than that for the 100K T antigen, with the apparent size difference being 250 nucleotides This finding is consistent with the mRNA for the 17K T antigen corresponding to an almost complete copy of the early region while the mRNA for the 100K T antigen would lack the sequences between 0.59 and 0.54 map unit. By in vitro translation of SV40-specific RNA followed by immunoprecipitation we have been unable to detect the synthesis of any T antigen intermediate in size between the 100K and 17K T antigens. We have demonstrated the synthesis of two proteins from intracellular SV40-specific mRNAs which appear to be identical to the VP2 and VP3 found in the virion on the basis of their mobilities in acrylamide gels and their tryptic peptide maps. Both VP2 and VP3 are labeled with formyl-[35S]methionine when synthesized in the presence of [35S]fMet-tRNAfMet. By analyzing partial proteolysis products of such N-terminally labeled proteins we could show that VP2 and VP3 share common C-termini. Therefore, VP3 is initiated and made independently of VP2 and is not derived from VP2 by proteolytic processing. VP2 and VP3 are both made from mRNAs about 19 S in size. The mRNA for VP2 migrates marginally more slowly than the mRNA for VP3 in acrylamide gels. © 1979.