Simian virus 40 tumor antigen: isolation of the origin-specific DNA-binding domain

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Abstract
To localize the origin-specific DNA-binding domain on the SV40 tumor (T) antigen molecule, limited proteolysis with trypsin was used to generate fractional peptides for analysis. A 17,000 MW peptide was found to be capable of binding not only to calf thymus DNA, but also specifically to the SV40 origin of DNA replication. This .apprx. 130-amino acid peptide was derived from the extreme N-terminus of the T antigen and represented < 1/5 of the entire molecule. The coding sequence for this tryptic peptide was located at .apprx. 0.51-0.67 map units (excluding the intron, which maps at 0.54-0.59). Since the first 82 amino acids are shared between large T and small t antigens, and since the latter does not bind DNA, it can be concluded that the sequence between isoleucine 83 and approximately arginine 130 is necessary for origin-specific binding by the T antigen. In vivo phosphorylation of the T antigen within this region completely abolished the ability of the 17,000 MW peptide to bind DNA. Evidently, DNA binding by the T antigen is regulated by posttranslational modifications.