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pubmed:abstractText |
Metabolic changes have been investigated during continuous growth of yeast cells inoculated in glucose-containing medium until the cells entered the stationary phase in response to glucose exhaustion. Well in advance of glucose exhaustion, a transition phase was observed, characterized by a decrease in the growth rate and a progressive reduction of protein and RNA accumulation. Two-dimensional gel analysis of the proteins synthesized during this stage showed that the pattern of proteins remained similar to that of log-phase cells. When the cells entered the stationary phase, protein accumulation was 10% of that in log-phase cells, and incorporation of labeled RNA precursor was undetectable. Analysis of protein synthesis gave evidence that the synthesis of 95% of the proteins present in log-phase cells was arrested in stationary-phase cells. Among the 20 proteins whose synthesis continues throughout the stationary phase were identified actin, aldehyde dehydrogenase, enolase, hexokinase, glyceraldehyde-3-phosphate dehydrogenase, and five heat shock proteins. In addition, the synthesis of six new proteins was observed. The occurrence of these new proteins in stationary-phase cells is presumed to result from the release of carbon catabolite repression due to glucose exhaustion.
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