Amino-terminal amino acid sequence of the major structural polypeptides of avian retroviruses: sequence homology between reticuloendotheliosis virus p30 and p30s of mammalian retroviruses.

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Abstract
The major structural polypeptides, p30 of reticuloendotheliosis virus (REV) (strain T) and p27 of avian sarcoma virus B77, were compared with regard to amino acid composition, NH2-terminal amino acid sequence and immunonological crossreaction. The amino acid composition of the 2 polypeptides is distinct, and a comparison of the first 30 NH2-terminal amino acids of REV p30 with that of the first 25 of B77 p27 yields only 3 homologous residues. In competition radioimmunoassays the polypeptides show no crossreactivity. A comparison of the amino acid composition and NH2-terminal amino acid sequence of REV p30 with those reported for several mammalian retrovirus p30 shows remarkable similarities. Both REV and mammalian p30 contain a large number of polar residues in their amino acid composition and show approximately 40% homology in the first 30 NH2-terminal amino acids. No crossreactivity could be observed in competition radioimmunoassays between Rauscher murine leukemia virus p30 and that of REV. The observations reported here suggest a close evolutionary relationship between REV and the mammalian retroviruses.