A 13-amino-acid Pit1-specific loop 4 sequence confers feline leukemia virus subgroup B receptor function upon Pit2

Feline leukemia virus subgroup B (FeLV-B) and gibbon ape leukemia virus (GA LV) utilize the human protein Pit1 but not the related protein, Pit2, as re ceptor. A stretch of 9 amino acids, named region A, was identified in the p utative fourth extracellular loop of Pit1 (residues 550 through 558) as cri tical for FeLV-B and GALV receptor function. However, the presence of Pit1 region A did not confer receptor function for FeLV-B upon Pit2, while it di d so for GALV. We have here shown that the presence of two Pit1-specific lo op 4 residues (tyrosine 546 and valine 548) in addition to Pit1 region A is sufficient to make Pit2 an efficient FeLV-B receptor; that is, a stretch o f 13 amino acids encompassing all loop 4 amino acid differences between Pit 1 and Pit2 comprises a C-terminal determinant for FeLV-B receptor function. Thus, the same limited receptor region is sufficient to confer receptor fu nction for both viruses upon Pit2.