Three independent polyproteins coded by the gag gene of type-D retrovirus in a continuous human cell line

The processing of gag-gene-coded polyproteins of type D retrovirus (HEp-2 V) in chronically infected continuous human larynx carcinoma cell line HEp-2 (HeLa-like) was investigated by means of the pulse-chase modification of the radioimmunoprecipitation test. Three independent polyproteins coded by the gag gene of HEp-2 V were revealed in the immunoprecipitates: Pr 78gag, a direct precursor of the virus internal structural polypeptides, described in a previous report (1); Pr 180gag + pol, a probable reverse transcriptase precursor; and gPr 78gag, a glycosylated polyprotein of unknown function. Two unstable intermediate polyproteins derived from Pr 78gag cleavage were detected in the presence of serine protease inhibitors. These polypeptides, having molecular weights of 37 K and 33 K, are Pr 37gag and Pr 33gag respectively. A probable scheme of gag-gene-coded polyproteins processing is suggested, and speculations on the gag-gene-coded glycosylated polyproteins of retroviruses as growth factor receptors are also presented.