We have sequenced the envelope genes from each of the five members of the gibbon ape leukemia virus (GALV) family of type C retroviruses. Four of the GALVs, including GALV strain SEATO (GALV-S), were originally isolated from gibbon apes, whereas the fifth member of this family, simian
sarcoma-associated virus (SSAV), was isolated from a woolly monkey and shares 78%
amino acid identity with GALV-S. To determine whether these viruses have identical host ranges, we evaluated the susceptibility of several cell lines to either GALV-S or SSAV
infection. GALV-S and SSAV have the same host range with the exception of Chinese hamster lung E36 cells, which are susceptible to GALV-S but not SSAV. We used retroviral vectors that differ only in their envelope composition (e.g., they contain either SSAV or GALV-S envelope
protein) to show that the envelope of SSAV restricts entry into E36 cells. Although unable to infect E36 cells, SSAV infects GALV-resistant murine cells expressing the E36-derived viral receptor, HaPit2. These results suggest that the receptors present on E36 cells function for SSAV. We have constructed several vectors containing GALV-S/SSAV chimeric envelope
proteins to map the region of the SSAV envelope that blocks
infection of E36 cells. Vectors bearing chimeric envelopes comprised of the N-terminal region of the GALV-S SU
protein and the C-terminal region of SSAV infect E36 cells, whereas vectors containing the N-terminal portion of the SSAV SU
protein and C-terminal portion of GALV-S fail to infect E36 cells. This finding indicates that the region of the SSAV envelope
protein responsible for restricting SSAV
infection of E36 cells lies within its amino-terminal region.