As a necessary part of the measurement of the time course of Incorporation of a specific precursor of RNA, 14C-uridine, into the various species of cellular RNA a study of the role of the metabolic pool has been carried out. 2-14C-uridine was rapidly incorporated by suspension cultures of Acer pseudoplatanus L. over a wide range of concentrations. A substantial proportion was incorporated specifically into RNA without measurable delay whilst the remainder equil-ibrated with a large pool of phosphorylated compounds within the cell. In addition, as the external concentration of 2-14C-uridine was increased, an increasing proportion of the uridine entering the cells was rapidly degraded with release of 14Co2 from culture. The pattern of labelling of RNA throughout the growth cycle has indicated that a large proportion of the total cellular content of RNA is turned over daring one cell generation time in batch cultures and that there are separate pools for RNA precursor molecules and degradation products. Investigation of the time course of incorporation of 2-14C- uridine into the various species of total RNA, fractionated by sucrose density gradient sedimentation and by gel electrophoresis, in actively dividing cell cultures has revealed the presence of several distinct species of rapidly labelled high molecular weight nuclear RNA which have been tentatively identified as precursors to ribosomal RNA. One of these RNA components has an estimated molecular wight of 3.8 x 106 daltons which is much greater than any yet reported in higher plant tissues. A culture system in which cells can be maintained in synchronous cell division for several full cell cycles has been described. Measurement of the changes in the rates of incorporation of labelled thymidine, uridine and leucine through the cell cycle have shown that they correlate, in general, with changes in the rates of accumulation of total DNA, RNA and protein. An S phase of from 30-35 hours was indicated and there was evidence of peaks of RNA synthesis after mitosis and after cytokinesis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:674036 |
| Date | January 1971 |
| Creators | Cox, Brian John |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/35443 |
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