Effects of the cellular p53 protein on Simian‐virus‐40‐T‐antigen‐catalyzed DNA unwinding in vitro

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Abstract
It is known that large T antigen, the regulatory protein encoded by Simian virus 40 (SV40), forms tight complexes with the cellular p53 protein in SV40‐transformed rodent cells. Using immunoaffinity procedures we have purified large T antigen and, in separate experiments, the cellular p53 protein. The two proteins formed complexes in vitro which bound well to double‐stranded DNA fragments although in a sequence‐unspecific manner. Free, uncomplexed T antigen readily converted double‐stranded DNA into a single‐stranded form whereas in‐vitro‐formed p53–T‐antigen complexes were inactive in this reaction. We conclude that one function of p53 in SV40‐transformed mouse cells could be the inhibition of the replication initiating activity of T antigen.