NEW CASE OF C-SRC GENE TRANSDUCTION - THE GENERATION OF VIRUS PR2257

PR2257 is a new replication-defective avian sarcoma virus which harbou rs in addition to the spliced version of the c-src gene also about 950 bp of no-coding cellular sequences located downstream from the c-src stop codon (Geryk et al., 1989). Comparison of the 950 bp region trans duced by PR2257 with the chicken c-src cDNA (Dorai et al., 1991) and g enomic sequences of the c-src 3' non-coding region from chicken and qu ail has shown that there are no additional introns. The c-src 3' mon-c oding region represents the largest c-src exon (No. 12) comprising abo ut 2 kb. Absence of conserved open reading frames within this region i n chicken and quail genomic DNAs excludes the possibility foe coding a protein by these sequences. Also, the possibility was excluded that n umerous endogenous virus-derived sequences identified in molecularly c loned PR2257 provirus played a role in the c-src transduction. After s erial passaging of PR2257 virus in vivo a variant PR2257/16 was isolat ed. In PR2257/16, the size of the env gene was increased due to homolo gous recombination with a helper virus. In addition to mutations in th e viral leader and the v-src coding region, a large deletion in transd uced c-src 3' non-coding sequences was found in the PR2257/16 genome. The significance of genome modifications for selective advantage of th is viral variant in vivo is discussed.