Discrete Regions ofSimian Virus 40LargeTAntigen Are Required forNonspecific andViral Origin-Specific DNA Binding

Thenondefective adenovirus type2 (Ad2)-simian virus 40(SV40) hybrid viruses, Ad2+ND2andAd2+ND4, havebeenusedtodetermine which regions of theSV40genomecoding forthelarge tumor(T)antigen areinvolved inspecific andnonspecific DNA binding. Ad2+ND2encodes 45,000 Mr(45K) and56,000 Mr (56K) Tantigen-related polypeptides. The45Kpolypeptide didnotbindtoDNA, butthe56Kpolypeptide boundnonspecifically tocalf thymus DNA.Ad2+ND4 encodes 60,000 Mr(60K), 66,000 Mr(66K), 70,000 Mr(70K), 74,000 Mr(74K), and 90,000 Mr(90K) Tantigen-related polypeptides, all ofwhich boundnonspecificallytocalf thymus DNA.However, inmorestringent assays, where tight binding to viral origin sequences wastested, onlythe90Kprotein specified byAd2+ND4 showed specific highaffinity forsequences attheviral origin ofreplication. From these results andpreviously published experiments describing theSV40DNA integrated intothese hybrid viruses, itwasconcluded thatSV40early gene sequences located between 0.39 and0.44 SV40mapunits contribute tononspecificDNA binding, whereas sequences located between 0.50and0.63SV40map units arenecessary forspecific binding totheviral origin ofreplication.