Presence of a hypervariable region within the hr2 domain of the host range determining sequences of the envelope protein gp85 (SU) of subgroup-A avian sarcoma-leukosis viruses

The nucleotide sequence of the gene for the envelope protein gp85 (SU) of the Schmidt-Ruppin subgroup A (NY) strain of Rous sarcoma virus [SRA(NY)] was determined, and the deduced amino acid sequence was compared with those of other avian sarcoma-leukosis viruses. Among the five host-range determinant sequences (vr1, vr2, hr1, hr2, and vr3), the host-range determinant sequence hr2 of SRA(NY) showed a significant deviation from the hr2 sequences of other subgroup A viruses, namely, RAV-1 and SRA(SF). A phylogenetic analysis of the amino acid sequence of this region indicated that this intra-subgroup diversity was as great as or even greater than the inter-subgroup diversity found among other subgroups of ASLV. Within the hr2 region, we found a short hypervariable segment that differs in length and sequence from hr2 of other subgroup-A viruses. The difference in the hr2 amino acid sequence between SRA(NY) and SRA(SF) is reflected in the predicted protein secondary structure of this region.