Kinetics of synthesis and processing of precursor polypeptides of murine leukemia virus in frog oocytes following microinjection of viral RNA.

Microinjection of Rauscher murine leukemia viral RNA into living oocytes from Xenopus 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 a 1-h labeling period were three precursor polypeptides of Mr 77000, 75000 and 65000. Following longer labeling periods the most stable precursor polypeptide of Mr 65000 was most prominent. In addition, several intermediates of Mr 35000--60000 were observed. After about 24 h, mature viral core proteins appeared. The rate of synthesis of the 75000-Mr and 77000-Mr 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 90000--95000-Mr polypeptides seemed to be post-translationally modified products of the 75000-Mr and 77000-Mr proteins. However, 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.