PRODUCTION OF DEFECTIVE VIRUS BY TERMINALLY DIFFERENTIATED MYOTUBES INFECTED WITH ROUS-SARCOMA VIRUS

The generally accepted concept that the replication of Rous sarcoma vi rus (RSV) is dependent on host cell DNA synthesis was reexamined. As t he host we used terminally differentiated myotubes (MT), in which no c ellular DNA synthesis is observed. As an extension of our previous stu dy which indicated that RSV-infected MT produce various virus componen ts, we examined viral particles produced by infected MT. Electron micr oscopy showed presence of viral particles released from infected MT. I mmunoprecipitation analysis revealed that these particles contained an equal amount of the gag but a decreased amount of the env proteins as compared with the particles from infected chicken embryo fibroblasts (CEF). Consequently, viral particles from infected MT had an infectivi ty only 6% of that of particles from infected CEF cells. In a parallel experiment, we microinjected molecularly cloned RSV DNA into MT. In c ontrast to the infection mediated by viral particles, both MT and CEF cells produced the same amount of infectious particles when microinjec ted with viral DNA. We conclude that RSV replicates in the complete ab sence of host DNA synthesis, though infectivity of the progeny virus d epends on the initial condition of the infection.