Kinetics of Synthesis and Processing of Precursor Polypeptides of Murine Leukemia Virus in Frog Oocytes following Microinjection of Viral RNA

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Abstract
Microinjection of Rauscher murine leukemia viral RNA into living oocytes from X. laevis, in contrast to cell-free systems, allowed detailed studies on the processing of newly synthesized viral precursor polypeptides. The viral messenger appeared to be stable for at least 5 days. Maximal rate of translation of 70-S virion RNA was observed 10 h after injection. The predominant translation products after 1-h labeling period were 3 precursor polypeptides of MW 77,000, 75,000 and 65,000. Following longer labeling periods the most stable precursor polypeptide of MW 65,000 was most prominent. In addition, several intermediates of MW 35,000-60,000 were observed. After about 24 h, mature viral core proteins appeared. The rate of synthesis of the 75,000-MW and 77,000-MW viral proteins decreased gradually after injection, suggesting that viral core polypeptides somehow regulated processing or synthesis of the group-specific antigen precursors. A heterogeneous group of 90,000-95,000-MW polypeptides seemed to be post-translationally modified products of the 75,000-MW and 77,000-MW proteins. In this study no envelope-related polypeptides were synthesized, when viral RNA (70-S or 35-S) was injected into the cytoplasm or the nucleus of Xenopus oocytes.