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The protease encoded by the human immunodeficiency virus (H1V) processes the viral gag and gag-pol protein precursor by posttranslational cleavage. In this study we have demonstrated by site-specific mutagenesis (Asp -* Thr) and by pepstatin A inhibition that the recombinant HIV protease is an aspartic-type protease. Furthermore, incubation of HIV-infected H9 cells with pepstatin A inhibited part of the intracellular processing of the HIV gag protein yet had no apparent toxicity on HIV-infected cells during 48 hr of incubation.

Rous sarcoma virus harvested from cells at intervals of 3 min has the same density, sedimentation coefficient, and DNA polymerase as virus harvested at hourly intervals. The RNA of the Prague strain-C consists of a minor class of 60-70 S RNA, a major class 30-40 S RNA, and a 4-12 S class of RNA present at variable concentration. The RNA of the Schmidt-Ruppin strain-A contains more 60-70S than 30-40S RNA. Upon incubation of virus harvested at 3-min intervals at 400 in cell growth medium or Trissaline, most of the 30-40S RNA is converted to 60-70S RNA.The electrophoretic mobility of the 30-40S RNA of the Rous virus harvested at 3-min intervals is lower than that of the 30-40S subunits of completely dissociated 60-70S RNA; after heating, their mobilities are identical. Heating also releases some small RNAs from 30-40S RNA of virus harvested at 3-min intervals, but five times more 4S RNA is released if the 30-40S RNA is allowed to convert to 60-70S in the virus. The template activity for Rous virus DNA polymerase of the 30-40S RNA of Rous virus harvested at 3-min intervals is about five times lower than that of 60-70S RNA. It is suggested that association of 30-40S RNAs with some RNAs of the 4-12S class may take place simultaneously with their conversion to 60-70S RNA.The RNAs of all known groups of RNA tumor viruses consist of a major 60-70S class and minor 4-12S class of polynucleotides (1, 2). The 60-70S RNA has a subunit structure (2). It can be dissociated into several major 30-40S RNAs (3-5) and several small heterogeneous and distinct RNAs (6, 7). There is also evidence that certain RNA tumor viruses contain, in addition to 60-70S RNA, free 30-40S RNA in the virion (8-10). Yet, free 30-40S RNA has not been observed in avian tumor viruses propagated under similar conditions. However, it was found recently that Rous sarcoma virus (RSV), an avian tumor virus, if harvested from cells at intervals of 5 min, contains heterogeneous RNA smaller than the 60-70S of virus harvested at hourly intervals (11). The RNA of such virus consisted of a principal 55-60S component, and several smaller components. Conversion of these RNA components to 60-70S RNA was not observed in purified virus (11).These notions, and in particular the one that virus liarvested at short intervals has an RNA different from virus harvested at long intervals (10,11), led us to ask whether a precursor form of the 60-70S RNA complex can be demoiistrated in the virion. We found that RSV harvested from infected cells at intervals of 3 mill contains three to six times more 30-40S RNA than 60-70S RNA, and that most of the 30-40S RNA may be converted to 60-70S RNA in the virion. We Abbreviation: RSV, Rous Sarcoma Virus.have also asked whether the viral 4-12S RNAs and the small RNAs associated with 60-70S RNA (6, 7) result only from partial degradation of 60-70S RNA in the virion as proposed by some (12), or whether at least a fraction of these small RNAs are present in virus freshly budded from infected cells. Recent studies in this laboratory indi...

The polypeptide precursor pr76 to the internal viral group specific (gs) antigen proteins of Rous sarcoma virus, synthesized in a cell-free system of ascites cells, has been processed in vitro into the viral proteins by purified viral protein p15 as well as by disrupted Rous sarcoma virus. Disrupted Rauscher murine leukemia virus does not stimulate the cleavage process in vitro. Autocatalytic cleavage of the polypeptide precursor pr76 of Rous sarcoma virus, which contains the peptide sequence of p15, is not observed. Virus specific proteins of several RNA viruses [polio virus, endomyocarditis virus, (1-4), Sindbis virus, Semliki Forest virus (5-8), and RNA tumor viruses (9-12)] are derived from larger polypeptide precursors by post-translational cleavage. Little is known about the agents involved in the cleavage process.

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