Transcriptional activity in previtellogenic oocyte germinal vesicles from Xenopus laevis

We have isolated germinal vesicles from previtellogenic Xenopus oocytes on a scale suitable for biochemical studies. The organelles were active in RNA synthesis, mainly mediated by endogenous RNA polymerase I. Nascent transcripts were 5-18S in size and complementary to DNA sequences present at intermediate reiteration frequency (several hundred copies per haploid genome). Hybridization to cloned 5S and 40S ribosomal genes demonstrated that the in vitro transcripts contained the latter, but not the former sequences in detectable amounts. The germinal vesicles also exhibited an ability to take up and retain UTP and a UTP-binding activity, probably protein(s), was extractable from the organelles with 0.35 M NaCl.