Uridine uptake by Schizosaccharomyces pombe is by a single step reaction with a Km of 3.15x10-5M. If the uridine concentration in the medium exceeds 2mM, uridine uptake appears to be chiefly by diffusion. The rate of uptake does not appear to limit the rate at which 3H-uridine is incorporated into RNA. In synchronous cultures, the rate of uridine uptake parallels the rate of its incorporation, but changes in the uptake rate occur 0.1 cell cycle after those in incorporation rate. The specific activity of the 3H-uridine pool in such cultures remains constant. Inhibitors which alter the relationship between the rates of uptake and RNA synthesis alter the size of the uridine pool. The relationship between pulse length and the distribution of 3R-uridine in various species of RNA was examined electrophoretically. After 1 min. of labelling, all radioactivity was in the ribosomal precursor, heterodisperse and 4-5 S RNA fractions. After pulses of 10 min or longer, label is distributed in essentially a steady-state labelling pattern. In synchronous cultures, the rate of RNA synthesis doubles at the time of DNA synthesis. When cultures are treated with the inhibitors of DNA synthesis, 2'-deoxyadenosine and 1-phenylethanol, they go through a period of adjustment during which the rate of RNA synthesis no longer is proportional to the DNA content of the cell. After cells have adjusted, however, the relationship between DNA and RNA synthesis is restored. Following a step-down in culture conditions the various RNA species are transcribed in approximately the same proportions as in control cultures. But the total rate of RNA synthesis is depressed and the processing of ribosomal precursor RNA is inhibited. The results are discussed and possible control mechanisms are considered.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662341 |
| Date | January 1976 |
| Creators | Staatz, William D. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14474 |
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