Characterization of Equine Infectious Anemia Virus gag Gene-encoded Proteins and the Complete Amino Acid Sequence of the Nucleic Acid Binding Protein.

Abstract

The gag proteins of equine infectious anemia virus (EIAV) were purified by reverse phase high pressure chromatography. The complete amino acid sequence of the nucleic acid binding protein (p11), as well as partial amino- and carboxy- terminal sequences of the other gag proteins (p15, p26, p9) was determined by chemical analysis on the purified proteins. The amino-terminal gag protein was blocked to Edman degradation. Immune Autoradiography allowed deduction of the gag gene order (p15-p26-pll-p9). These data provided partial confirmation of the nucleotide sequence of Stephens, et al. (132). The complete amino acid sequence of EIAV pll was determined and contained two sets of cysteine arrays. The cysteine array represents one of the most invariant amino acid sequences known to exist in retroviruses. Arrays contain conserved residues which include cysteines at positions n, n+3, n+13. It was postulated that the presence of an aromatic residue at positions n+1 or n+2 may be necessary for an array to be fully functional in binding viral RNA. The presence of a double set of "complete" cysteine arrays is correlated with the presence of the unusual rod shaped core characteristic of lentiviruses. A causal relationship is suggested. Analysis by fluorescent enhancement indicated a biphasic binding of EIAV pll to poly(etheno adenylic acid). The first stage of binding was non-cooperative, while the second stage involved cooperativity. It was concluded that EIAV pll might serve as a good model for studying the interactions of lentiviral nucleic acid binding proteins with RNA.