Tumour antigen specificity of a DNA-binding protein from cells infected with adenovirus 2

Abstract

Two new polypeptides of molecular weights 75,000 and 45,000 are found in KB cells infected with human adenovirus type 2 (Ad 2), (ref 1). They represent the major labelled protein components of a nuclear membrane fraction (‘DNA replication complex’) that is capable of synthesising adenovirus DNA in vitro^1–3. It has been proposed that these polypeptides are early viral gene products, for they are synthesised soon after infection in the presence of 1-β-D-arabinosylcytosine (Ara C), an inhibitor of DNA synthesis¹. Their association with the DNA replication complex suggested that they may have an affinity for DNA and could play a role in the replication of adenovirus DNA. It was subsequently shown that these two polypeptides bind strongly to single-stranded DNA–cellulose columns and that large amounts of these ‘DNA-binding proteins’ can be isolated from the cytoplasm of the infected cells². Two polypeptides of similar molecular weights (72,000 and 48,000) were independently isolated from cell extracts of monkey kidney cells, abortively infected with Ad 5, by their ability to bind to single-stranded DNA-cellulose^4,24. The use of temperature-sensitive mutants of Ad 5 indicated that these polypeptides are viral-coded^4,24. Comparison of tryptic maps suggested that the 48,000 component was a degradation product of the 72,000 polypeptide (A. J. Levine, unpublished). A polypeptide of molecular weight about 65,000–75,000 has also been detected by polyacrylamide gel analysis in KB cells soon after infection by Ad 2 and Ad 5 (refs 5–7) and in HeLa cells infected by Ad 2 (ref. 8).