Adenovirus chromatin I. Isolation and characterization of the major core protein VII and precursor Pro-VII.

The DNA core of adenovirus contains two basic polypeptides V and VII. The major core polypeptide VII (M, = 18,000) is histone-like and has been shown to be derived from a larger polypeptide Pro-VII (M, = 20,000) (Anderson, C. W.. Baum, P. R., and Gesteland, R. F. (1973) J. Virol. 12, 241). Chemical studies were initiated to investigate the processing of P-VII (Pro-VII) to VII in molecular detail. The two basic proteins were acid extracted from KB cell nuclei productively infected with adenoviruses. The proteins were separated on a phosphocellulose column and further purified by Sephadex G-75 column chromatography. The identity as well as the precursor and product relationship between the two isolated proteins were compared and verified by amino acid composition, end group determination, and chemical cleavages. The N-chlorosuccinimidelurea (NCSI urea) cleavage of VII generated two large polypeptide fragments which corresponded to the loss of 20 and 31 residues from both the NHBand COOH-terminal ends of the molecule. The same two large peptide fragments were also generated in the NCS/urea cleaved Pro-VII, thus confirming the relatedness of the two proteins. The location and nature of the precursor sequence was determined by comparing the NCSlurea-cleaved small NH,and COOH-terminal peptide fragments. The small COOH-terminal peptide fragments from both Pro-VII and VII had identical amino acid composition and end group. However, the small NH,-terminal peptide fragment from Pro-VII was approximately 20 residues larger than the NH,-terminal counterpart from VII. Thus. the processed fragment is located at the NH,-terminal end of Pro-VII and, in comparison to the remainder of the molecule, it has a unique amino acid composition. It is hydrophobic and may even be acidic (amide status unknown). The presence of this region in the Pro-VII. DNA complex and the subsequent processing to VII-DNA chromatin may be important in the “proper folding” of the adenovirus chromosome.