Avian erythroblastosis virus: transformation-specific sequences form a contiguous segment of 3.25 kb located in the middle of the 6-kb genome

Abstract

Several foci of chicken embryo fibroblasts transformed by avian erythroblastosis virus (AEV) strain ES-4 were found to produce virus progeny containing the RNA of the replication-defective AEV in excess over the RNA of the helper virus. The size of AEV RNA was determined by methylmercury-agarose gel electrophoresis and electron microscopy to be 28 S or 6 kb. About 40 to 45% of this RNA is homologous by RNA-DNA hybridization to the RNA of other chicken leukosis and sarcoma viruses; the rest of the genome is AEV specific. These AEV specific sequences, which presumably contain the genetic information responsible for transformation form a contiguous stretch of 3.25 kb, located by heteroduplex mapping in the center of the 6 kb genome between two segments of 1.06 kb at the 3′ end and 1.64 kb at the 5′ end which are homologous to the genome of avian sarcoma virus. From the length of the region showing homology between AEV and avian sarcoma virus at the 5′ end of the genome and from the known sequence composition of the AEV-specific 75K protein (Hayman et al., 1979), it can be deduced that the initiation point for the N terminus of the gag protein p19 is located about 1.0 kb from the 5′ end of the genome in avian oncoviruses. Nonproducing AEV-transformed chicken embryo fibroblasts were also isolated. Infectious AEV could be rescued from these cells only with chicken leukosis viruses; unrelated avian retroviruses were ineffective, probably because AEV requires complementation in the gag and pol genes, in addition to env.