Simian virus 40 (SV40)-specific isoelectric point-4.7--94,000-Mr membrane glycoprotein: major peptide homology exhibited with the nuclear and membrane-associated 94,000-Mr SV40 T-antigen in hamsters

Abstract

Tryptic peptide maps of electrophoretically purified 94,000-molecular weight (relative) (Mr) nuclear and membrane-associated simian virus 40 (SV40) T-antigens, TN and TM, respectively, were compared to those of the SV40-specific isoelectric point (pI)- 4.7--94,000-Mr plasma membrane component reactive with anti-T-sera from Syrian golden hamsters. Bidimensional thin-layer electrophoresis and chromatography of TN labeled with 125I revealed about 27 tryptic peptides. A similar number of peptides was identified for TM and the pI-4.7--94,000-Mr component. A peptide homology between TN and TM or TN and the pI-4.7-94,000-Mr protein exists and indicates that the previously described pI-4.7--94,000-Mr membrane component represents TM. Only 4 of 27 peptides were labeled when TM was subjected to lactoperoxidase-catalyzed radioiodination from the outer surface of the plasma membrane. One of these TM peptides was metabolically labeled with [14C]glucosamine. The data indicate that TM is partially exposed on the cell surface and represents a glycosylated form of TN. Closely associated with TM is a pI-4.5--55,000-Mr membrane component. This component does not exhibit significant peptide homology with the 94,000-Mr SV40 protein and, therefore, appears to be coded for by the host cell genome.