title: The binding of simian virus 40 large T antigen to the polyphosphate backbone of nucleic acids.
abstract: Simian virus 40 (SV40) large tumor antigen (T antigen), a phosphoprotein found in nuclei of SV40-infected and -transformed cells, binds nonspecifically to DNA. To study this mechanism the binding properties of T antigen to double-stranded (ds) and single-stranded (ss) DNA-cellulose as well as to phosphocellulose were compared. After incubation of [35S] methionine or [3H] leucine/[32 P] phosphate radioactively-labeled cell extracts at different pH values (6.0, 7.3, 9.0) with DNA- or phosphocellulose, bound and unbound species of T antigen were purified and analyzed by SDS-polyacrylamide gel electrophoresis for both the yield and the possible correlation with protein phosphorylation. T antigens bound with comparable affinities to ds- and ss-DNA-cellulose and phosphocellulose. These results suggest the binding of T antigen to the polyphosphate backbone of DNA as a molecular mechanism for its nonspecific binding. The evidence for this observation was supported by blocking the binding of T antigen to DNA-cellulose by divalent  cations (Ca2+, Mg2+). 3H/32P ratios of T antigen obtained by double-labeling cells for various times imply that higher phosphorylated forms of T antigen bound more strongly to ds- and ss-DNA as well as to phosphocellulose. Thus, in the presence of cellular proteins and other components the binding activity of T antigen to the polyphosphate backbone of DNA seems to be positively correlated with its phosphorylation. These observations are consistent with the hypothesis that the binding affinities of SV40 T antigen to host cell DNA may be regulated by its phosphorylation.
mesh_terms: D000956:Antigens, Viral / Q000378:metabolism*; D000957:Antigens, Viral, Tumor; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D002482:Cellulose / Q000031:analogs & derivatives / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004268:DNA-Binding Proteins; D010710:Phosphates; D010750:Phosphoproteins / Q000378:metabolism
chemical_list: D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D002352:Carrier Proteins; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D010710:Phosphates; D010750:Phosphoproteins; D002482:Cellulose; D004247:DNA; C008881:phosphocellulose