LOW-FREQUENCY PRODUCTION OF RECOMBINANT SUBGROUP-E AVIAN-LEUKOSIS VIRUSES BY UNINFECTED V-15B CHICKEN-CELLS

15B chicken contains V-15B an allele for the spontaneous production of a noninfectious avian leukosis virus, 15B-ILV. In this paper we present evidence that uninfected 15B cells also produce subgroup E viruses, designated 15B-E viruses. In contrast to 15B-ILV which occurs at an estimated frequency of one event per 103 15B cell days, 15B-E viruses occur at estimated frequencies of one event per 2 × 109 cell days. The frequency of occurrence of 15B-E viruses was affected by the level of expression of V-15B and the presence of endogenous viral alleles which constitutively express subgroup E envelope antigens. The proteins of nine independent isolates of 15B-E viruses were analyzed by SDS-polyacrylamide gel electrophoresis. All isolates had p27 proteins with the distinctive electrophoretic mobility of the p27 of RAV-0, an endogenous virus. Each isolate had characteristic pairs of p19 related proteins which were similar to pairs of p19 related proteins, which are generated by recombination of PR-RSV-C and RAV-0. Since 15B-E isolates occurred in uninfected cells and contained proteins which are characteristic of RAV-0 and recombinants of RAV-0, we suggest that 15B-E viruses are recombinants of endogenous virus information. Since the level of expression of V-15B and the presence of endogenous viral alleles which constitutively express subgroup E envelope antigens affected the frequency of occurrence of 15B-E viruses, we further suggest that 15B-ILV and RNAs which contain information for subgroup E envelope antigens are the parents of 158E viruses. © 1979.