A histone-like protein from adenovirus chromatin

Abstract

THE DNA in adenovirus is complexed with two viral specific polypeptides, VII and V, to form the compact core structure. There are 1,070 copies of VII (18,000 molecular weight) and 180 copies of V (45,000 MW) per viral genome of 36,000 base pairs¹. Cordon et al.² have suggested that the combination of six copies of VII, one copy of V and 200 DNA base pairs form the basic subunit structure of adenovirus chromatin. Such arrangement is also characteristic of the eukaryotic chromatin subunit which is composed of eight histones (two each of H2a, H2b, H3 and H4) and a unit DNA length of approximately 200 base pairs (see ref. 3 for review). The major core protein, VII is highly basic; almost 23 mole per cent of the residues are arginine^4–6. A simple calculation reveals that the mass ratio of VII: DNA is 1 : 1 which is similar to the histone : DNA ratio in eukaryotic chromatin. This suggests that polypeptide VII-DNA interaction may be similar to that of histones and DNA. Amino acid sequence studies have revealed an asymmetric distribution of basic residues in the histones. In particular, the amino end is highly basic and is implicated in DNA binding; the carboxy1 end is less basic yet more hydrophobic and is involved in histone–histone interactions^7,8. To determine if the amino end of VII is also basic, we isolated polypeptide VII from adenovirus type 2 in milligram yield⁹ and sequenced its amino end by automatic Edman degradation (Fig. 1). We present here a partial sequence determination.