Absence of a structural basis for intracellular recognition and differential localization of nuclear and plasma membrane-associated forms of simian virus 40 large tumor antigen.
The simian virus 40 large tumor antigen (T-ag) is found in both the nuclei (nT-ag) and plasma membranes (mT-ag) of simian virus 40-infected or -transformed cells. It is not known how newly synthesized T-ag molecules are recognized, sorted, and transported to their ultimate subcellular destinations. One possibility is that these events depend upon structural differences between nT-ag and mT-ag. To test this possibility, we compared the structures of nT-ag and mT-ag from simian virus 40-infected cells. No differences between the two forms of T-ag were detected by migration in polyacrylamide gels, by Staphylococcus aureus V8 partial proteolytic mapping of methionine- or proline-containing peptides, or by two-dimensional tryptic peptide mapping of methionine-containing peptides. The carboxy-terminal, methionine-containing tryptic peptide was identified in the two-dimensional maps and was shown to be identical in nT-ag and mT-ag. Thus, a structural basis for the recognition and differential localization of T-ags could not be demonstrated. The carboxy terminus of the T-ag encoded by mutant dlA2413 is derived from the alternate open reading frame of the simian virus 40 early region, in analogy with the theoretical early gene product, T*-ag. We used this mutant to identify peptides unique to T*-ag. None of these peptides were detected in maps of mT-ag; only wild-type T-ag-specific peptides were found. These findings suggest that T*-ag does not represent the membrane-associated form of T-ag, but that mT-ag is encoded within the same reading frame used for nT-ag.
D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000235:genetics* / Q000302:isolation & purification; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D002467:Cell Nucleus / Q000201:enzymology*; D002472:Cell Transformation, Viral; D008715:Methionine / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000235:genetics* / Q000302:isolation & purification; D010446:Peptide Fragments / Q000032:analysis; D011494:Protein Kinases / Q000235:genetics*; D013539:Simian virus 40 / Q000235:genetics*
D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D010446:Peptide Fragments; D008715:Methionine; D011494:Protein Kinases