Complete env gene deletions of three replication-defective strains of Rous sarcoma virus and a model for the origin of their genetic structures

Abstract

Replication-defective deletion mutants of Rous sarcoma virus (RSV) have been described which transform cells in culture and elaborate envelope (−) defective particles. The env deletions of two clonal variants of the Bryan strain of RSV, RSV(−)3, and RSV(−)16, and of a replication-defective variant of Schmidt-Ruppin RSV (SRN8) were analyzed by fingerprinting oligonucleotides hybridized by a molecularly cloned env DNA probe that spans from near the 3′ end of pol to the 3′ end of env. It was observed that all three replication-defective RSV strains are essentially complete env deletions but retain the 3′ end of pol. Based on a common pol-src junction oliogonucleotide that may reflect a homologous sequence repeated at both ends of env in nondefective RSV, the env deletions of RSV(−)3 and 16 appear to be isogenic. The original deletion may have involved recombination between these sequences. The absence of this oligonucleotide in SRN8 indicates that the env deletion of SRN8 has different borders and represents an independent env deletion of nondefective RSV. All three defective RSVs have the genetic structure gag-pol-src. This genetic structure is consistent with the need for a complete gag to make a particle and with the assumption that an independent src gene rather than a gag- or gag-pol-src hybrid gene functions in transformation. It is suggested that a complete pol is not necessary for, but may assist, virus particle formation.