No abstract

Large deletion (LD) mutants of Prague strain Rous sarcoma virus subgroup B (PrB), derived by serial undiluted passage through chicken (C/E) cells, contain two deletions relative to wild-type virus. One of these joins gag sequences in the p12 coding region to env sequences in region encoding gp37; the other deletion spans the src region. Analysis of the viral proteins of QT6 cell clones containing only LD proviruses by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major truncated gag-related phosphoprotein of 60,000 to 66,000 daltons (P63LD). P63LD was stable, but could be cleaved in vitro to the predicted products by p15gag. A second gag-related LD protein of about 68,000 to 74,000 molecular weight (P7OLD) was also found which often reacted with an anti-gp37 serum. P7OLD was unstable and may represent a short-lived gag-gp37 fusion protein. Finally, immunoprecipitation indicated that particles containing P63LD were shed from QT6-LD clones. Thin section preparations of these clones viewed in an electron microscope showed enveloped budding particles of "immature" morphology. Thus, the synthesis and release of particles from infected cells does not require cleavage of the gag precursor, nor does it require the presence of p15 or (most of) p12.

Large deletion (LD) mutants of Prague strain Rous sarcoma virus, subgroup B (PrB), derived by serial undiluted passage through chicken (C/E) cells, were isolated and characterized. Individual LD viruses were initially isolated by cloning in soft agar of infected, chemically transformed quail (QT6) cells. Two regions of the PrB genome were deleted in the formation of the LD virus. This resulted in the junction of gag sequences in p12 to env sequences in gp37, and in the loss of the src gene. DNA restriction analysis of biologically active A Charon 27-LD recombinant clones indicated that individual LD viruses contained similar but not identical deletion endpoints. Two LD isolates, LD25 and LD85, were further subcloned into pBR322, and the deletion junctions were examined by DNA sequencing. Although the gag-env deletion endpoints were identical in the two subclones, heterogeneity was observed across the src deletion in that both mutants analyzed had the same 5' endpoint but slightly different 3' endpoints. In all cases, only a single homologous base (always an A residue) was found at the deletion endpoint. Si nuclease analysis of the RNA from a number of QT6-LD clones gave similar results, indicating that the LD population was composed of viruses with similar but not identical deletion endpoints. Such viruses may have been generated from errors during reverse transcription of the virion RNA with subsequent selection assuring their dominance in the population.