Rates of RNA synthesis, and in particular poly(A) +RNA synthesis, in oocytes of Xenopus laevis have been measured by analysing the kinetics of incorporation of exogenous radioactive nucleoside, or of microinjected radioactive nucleoside triphosphate, into TOA precipitable material coupled with determinations of precursor pool specific activity. Poly(A) RNA was isolated by oligo (dT)cellulose chromatography. Stable RNA, over 80% of which was rRNA, was synthesized in stage 6 oocytes and accumulated in the cytoplasm at a constant rate of 650 pg/oocyte/hour for at least 100 hours. By isolating germinal vesicles, it was shown that more than 70% of the RNA synthesized initially in stage 6 oocytes was unstable nuclear RNA with a half-life shorter than 4 hours, much of which sedimented heterogeneously on sucrose gradients. In stage 6 oocytes all the poly(A) RNA which was synthesized at an initial rate of 30 pg/oocyte/hour appeared to turn over with an average halflife of 10 hour and the steady state amount accumulated was 0.5% of the stored pool of poly(A) RNA. Similar kinetics were observed in enucleated oocytes but othidium bromide inhibited poly (4) RNA synthesis by about 70%. These observations suggest that much of the poly(A) RNA synthesis in stage 6 Xenopus laevis oocytes is mitochondrial. Stage 1 oocytes synthesized stable RNA at a constant rate of 17 pg/oocyte/hour for at east 80 hours and over 80% of the RNA accumulated was 4S and 53 RNA. Poly(A) RNA, with slightly different sedimentation properties and poly(A) size from that in stage 6 oocytes, was synthesized at an initial rate of 0.7 pg/oocyte/hour most of which was unstable, having a half-life of about 12 hours. The discussion relates these rate measurements to the known patterns of RNA accumulation during oogenesis and the mechanisms of transcription of maternal mRNA and other RNA classes.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663117 |
| Date | January 1978 |
| Creators | Turner, Philip C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11470 |
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