Structural and Antigenic Analysis of the Nucleic Acid Binding Proteins of Bovine and Feline Leukemia Viruses

Abstract

The nucleic acid binding proteins of bovine leukemia virus (BLV) and feline leukemia virus (FeLV) were isolated in a high state of purity with chloroform-methanol extraction followed by reversed-phase liquid chromatography. Selective solubilization of the nucleoproteins BLV p12 and FeLV p10 was confirmed also by SDS-polyacrylamide gel electrophoresis. The compositions and molecular weights were determined by amino acid analysis. BLV p12 has a molecular weight of 6,034 and FeLV p10 a molecular weight of 5,652 (minus cysteine and tryptophan for both proteins). Their compositions indicate an abundance of lysine and arginine residues which along with their size identified both as small basic proteins similar to well defined type C viral nucleoproteins. A single microsequencing analysis of each protein by semi-automated Edman degradation determined the sequence of the first forty amino acids. The putative nucleic acid binding site found in several type C viral nucleoproteins was contained within this sequence with the most homology centered around an eight amino acid region. Carboxyl -terminal amino acids were determined by digestion with carboxypeptidase A. Antiserums specific for the nucleoproteins were developed in rabbits. The specificity and titers were determined by electroblotting and immunoautoradiography. Both antiserums indicated cross reaction between nucleoproteins. Because of both their specific homologous reaction and their additional cross reaction the presence of more than one antigenic site on each protein is indicated. The antigenic site where cross reactivity occurs may exist in the conserved eight amino acid region within the nucleic acid binding site of the proteins.