Translation of avian type C virus messenger RNA: evidence for multiple initiation sites.

The avian sarcoma virus genome has been shown to consist of four genes arranged in the following order: 5′-gag pol-env-src-3′. In the present study, the pol gene product was found to be expressed in avian tumor virus-infected cells at several-hundred-fold lower levels than the translational products of the gag and env genes. Moreover, a translational block or possible deletion involving the carboxy-terminal region of the gag gene in chicken embryo cells had no apparent influence on the level of expression of the env gene. These findings indicate the involvement of multiple initiation sites for translation of the avian type C viral genome.