Restricted addition of proviral DNA in target tissues of chickens infected with avian myeloblastosis virus.

Proviral DNA is synthesized within an hour after infection of chicken cells with an avian oncornavirus and is integrated into nuclear cellular DNA within a short time. The viral DNA appears to be synthesized as double-stranded molecules of approximately 6 X 10(6) daltons some of which are converted into supercoiled cricles perhaps as a requisite for integration. The endogenous v-DNA in normal chicken cells and both the endogenous and amv v-DNA in leukemic chicken myeloblasts are covalently linked with chromosomal DNA. There is no detectable free DNA either circular or linear present in leukemic cells several weeks after infection. The endogenous v-DNA which is transmitted vertically from parents to offspring is uniformly and stably distributed in all chicken organs. There are about 1-2 copies of endogenous provirus per haploid genome of all normal cells. This DNA is very closely related to RAV-O RNA. After infection with AMV it seems that target cells such as leukemic myeloblasts, RBC and nephroblasts acquire complete copies of AMV DNA. Interestingly, only these target cells can be converted to neoplastic cells in the chicken as well as in vitro. The target cells acquire 1-2 copies of AMV specific DNA per haploid genome in addition to the endogenous v-DNA. All the available evidence shows that leukemic and kidney tumor cells have acquired AMV v-DNA. It remains to be elucidated whether the newly added viral DNA is alone responsible for neoplastic changes or does so in conjunction with endogenous viral information.