Production of env-deficient rous sarcoma virus (RSV) early after infection

Production of defective virus particles during the early stage of Rous sarcoma virus (RSV) infection of chicken embryo fibroblasts (CEF) was examined. RSV harvested 2 days post infection (2pi) had 10 to 30 times lower specific infectivity (focus forming units/unit reverse transcriptase activity) than 5pi harvest. Virus particles produced on day 2 contained less env proteins than particles harvested on day 5. The amount of other viral proteins was equal in particles harvested on day 2 and day 5. Analysis of infected cells revealed that these cells synthesized less env proteins on day 2 than on day 5. RSV RNA in infected cells was spliced normally on day 2. Infection at a low multiplicity of infection (moi) prolonged the production of defective particles. When infection was initiated by a low moi (0.01), particles harvested on day 5 had the same characteristics as 2pi particles after infection with a high moi (1.0). We conclude that the low infectivity of early harvest is due to the reduced amount of env proteins in virus particles, which is a consequence of the reduced env protein synthesis.