Comparison of immature (rapid harvest) and mature Rous sarcoma virus particles

Abstract

RSV-Prague was harvested from transformed chick embryo fibroblasts 5, 10, 20, 60, and 180 min after release and compared with virus harvested after 12 and 24 hr with respect to the nature of its RNA, polypeptide constitution, and ability to use its own RNA and added DNA as primer/template for DNA synthesis. The following results were obtained: 1. a. Immature (5 min) virus contained little 68S RNA. The principal component of the native RNA of such virus was rather heterogeneous, with a median sedimentation coefficient of 55–60S; in addition, several other components were also present. In the denatured state immature virus RNA consisted of approximately equal parts of very homogeneous 36S RNA, RNA which sedimented between 36S and 4S, and 4S RNA. By contrast, the native RNA of mature (24 hr) virus consisted mostly of a homogeneous 68S component, which on denaturation yielded a heterogeneous population of molecules sedimenting between 36S and 4S. The RNA of virus at intermediate stages of maturity yielded profiles intermediate between these two patterns. 2. b. Immature (5 min) virus particles contained 26 readily identifiable polypeptides; mature (24 hr) virus particles contained only 13. Virus particles of intermediate age contained intermediate numbers of polypeptides. No precursor—product relationships were discernible; rather, it appeared that 13 polypeptides were lost during maturation and aging. 3. c. The ability of immature (5 min) virus particles to synthesize DNA was not enhanced by the addition of detergent (Triton X-100); on the other hand, the addition of calf thymus DNA as exogenous primer/template profoundly stimulated DNA synthesis. The reverse was true for mature 24-hr virus. This suggested that the location of the enzyme(s) responsible for DNA synthesis differed in immature and mature virus particles, and implied that the RNA of immature virus particles might not be in the proper configuration necessary for serving as a primer/template for DNA synthesis.