Coupled transcription-translation of silkworm cytoplasmic polyhedrosis virus injected into oocytes of the frog, Xenopus laevis.

The cytoplasmic polyhedrosis virus of the silkworm, Bombyx mori, contains a ten-segmented, double-stranded RNA genome and five species of polypeptides, V1 (Mr 146,000), V2 (Mr 140,000), V3 (Mr 128,000)), V4 (Mr 62,000), and V5 (Mr 32,000). The virus contains an RNA-dependent RNA polymerase that transcribes the duplex genome RNA to form mRNA either in the infected animals or under appropriate conditions in vitro. We co-microinjected the virus, [alpha-32P]GTP and actinomycin D into oocytes of the frog, Xenopus laevis, and found that at least eight species of mRNA were formed in the oocytes. Virus-injected oocytes were labeled with [35S]methionine and cell extracts were treated with rabbit anti-cytoplasmic polyhedrosis virus immunoglobulin G. Analysis of the immunoprecipitates by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that V1, V2, and V3 were produced in the virus-injected oocytes whereas V4 and V5 were not. By injecting the separated double-stranded genome segments immediately after heat-denaturation into oocytes, it was found that V1 was coded for by segment 1 with a chain length of 4.2 kilobase pairs, V2 by segment 2 or 3, whose chain lengths are both 4.0 kilobase pairs, and V3 by segment 4 with a chain length of 3.2 kilobase pairs. These results demonstrate that the Xenopus oocyte is a very useful system for the coupled transcription-translation of double-stranded RNA viruses.