We examined the kinetics of accumulation and processing of simian virus 40 (SV40) RNA in stage 6 oocytes of
Xenopus laevis
microinjected intranuclearly with SV40 DNA. The rates of synthesis and degradation, cellular distribution, size, and sequence specificity of radiolabeled SV40-specific and endogenous oocyte RNA were determined. The kinetics of accumulation of SV40 RNA were biphasic, with greater than 90% of the viral RNA turning over in the nucleus with a half-life of 20 to 40 min. Although most of the primary transcription products were multigenomic in length, some stable polyadenylated SV40-specific RNA similar in size and sequence to late 19S mRNA accumulated in the cytoplasm with time. Differences in strand preference, efficiencies of transcription termination and polyadenylation, and the splice sites used in the synthesis and processing of SV40 RNA in
Xenopus
oocytes and monkey cells were noted. However, these differences were quantitative, rather than qualitative, in nature. Consequently, they are probably due to regulatory rather than mechanistic differences between the two cell types. We therefore conclude that
Xenopus
oocytes may be a useful system for studying both mechanistic and cell type-specific regulatory aspects of mRNA biogenesis from cloned DNAs. However, since only a small percentage of the initially synthesized RNA ends up in stable mRNA, it will be important to determine whether mutants of cloned DNAs that produce abnormal amounts of stable mRNAs are altered in promotion and initiation of RNA synthesis, transcription termination, RNA processing, or the stability of the resultant mRNAs.
Synthesis and maturation of Xenopus laevis methionine tRNA gene transcripts in homologous cell-free extracts.