title: Self-assembly of simian virus 40 large T antigen oligomers by divalent cations.
abstract: In simian virus 40-transformed cells, simian virus 40 large T antigen can be detected in different forms separable by sucrose density gradient centrifugation. In our experiments, light forms sedimented around 5 to 7S, oligomers such as tetramers were detected around 16S, and higher aggregates sedimented in a broad distribution reaching above 23S. The oligomers sedimenting at and above 16S could be disassembled into the slowly sedimenting 5 to 7S forms by chelating agents [EDTA or ethylene bis(oxonitrilo)tetraacetate]. After the addition of divalent cations (CaCl2 or MgCl2) in excess of chelating agents, oligomeric forms reassembled and appeared in a sedimentation pattern resembling that observed before treatment with chelating agents. Time course studies permitted the identification of the 5 to 7S forms as precursors upon pulse-labeling (15 min); the 16S and higher oligomers were identified as the successors after a 14-h chase. Treatment of extracts of pulse-chase-labeled cells with chelating agents again disassembled the oligomers, whereas pulse-labeled precursors did not change their 5 to 7S sedimentation pattern. Adding an excess of divalent cations reassembled the pulse-chase-labeled T antigen to oligomers but did not influence the sedimentation behavior of pulse-labeled 5 to 7S precursors. It is therefore reasonable to assume that a posttranslational modulation induces divalent cation binding, leading finally to the oligomerization of T antigen. Thus, some of the multifunctional activities of T antigen can be dictated by divalent cation binding properties.
mesh_terms: D000956:Antigens, Viral / Q000378:metabolism*; D000957:Antigens, Viral, Tumor; D002118:Calcium / Q000494:pharmacology*; D002499:Centrifugation, Density Gradient; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational; D013539:Simian virus 40 / Q000187:drug effects / Q000254:growth & development / Q000276:immunology*
chemical_list: D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D046911:Macromolecular Substances; D008274:Magnesium; D002118:Calcium