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 Hamsters23

Abstract

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