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The status of glyoxalase-I was explored in exponentially growing and G1arrested temperature sensitive (ts) cell division cycle (cdc) mutants of Saccharomyces cerevisiae. It was observed that the specific activity of this enzyme was correlated with overall growth status. The activity was high in actively growing cells and was low in G1arrested cells. Specific activities of glyoxalase-I were also low in G1arrested prolonged stationary phase (PSP) cells of S. cerevisiaeand Candida albicans. The activity of glyoxalase-I recovered when G1arrested S. cerevisiae(ts) cells were allowed to regrow under permissive conditions. Results demonstrate that although glyoxalase-I activity is a good indicator of cell growth status, it is not involved in cell cycle regulation of this eukaryotic organism.

It was shown that the decrease in phosphatidylinositol (PI) content in cdc 28 G 1-cells was due to a defect in inositol transport. This decrease in inositol transport was linked to microtubular function which was evident by the effect of a microtubular disrupting agent (colcemid) on inositol transport in stationary phase A364A cells. The involvement of PI in yeast G 1phase was further substantiated by the observation that o-phenanthroline, which blocks yeast cells in G 1phase, could inhibit inositol transport and PI levels as well. It is proposed that the regulation of PI metabolism is mediated by the gene cdc 28 and that microtubules may play a major role in the mechanism of action of this gene product.

The toxicity of the protein synthesis inhibitor puromycin towards a number of human and Chinese hamster cell lines has been examined. In comparison to cells of human origin, Chinese hamster cells exhibited about 25-fold higher resistance towards puromycin. These differences appeared to be species related as all the cell lines from any one species showed similar sensitivity towards puromycin. The incorporation of [ 3H]leucine in the hamster cell lines was accordingly found to be more resistant to the inhibitory effects of puromycin as compared to human cells. Studies on the cellular uptake of [ 3H]puromycin showed that in comparison to human cells, the drug uptake/binding in the hamster cell lines was greatly reduced. However, protein synthesis in the extracts of hamster and human cells showed no significant differences in sensitivity towards puromycin. These results show that the observed species related differences in cellular toxicity to puromycin are due to differences in the cellular uptake/binding of the drug.

Individual phospholipids were assayed in exponentially growing and G 1-arrested temperature-sensitive cell division cycle ( cdc) mutants of Saccharomyces cerevisiae. It was observed that cdc28 cells which are known to arrest at ‘start’ when shifted to their non-permissive temperature, resulted in a 40% decrease in phosphatidylinositol (PI) level while the phosphatidylserine (PS) content was doubled in these cells. The reduced level of PI was restored in cdc4 and cdc7 mutants which are known to arrest past the ‘start’. The increase in PS level in cdc8 mutant which was probably to compensate the intrinsic charging of membrane environment, was also reduced in cdc4 and cdc7 mutants. Our results demonstrate that PI may play a role in yeast cell division and growth that the abnormalities of cdc28 could also be related to PI decrease.

MicrotubuleProtein kinaseGrowth controlG 1arrest Cell cycleSaccharomyces cerevisiae

Individual phospholipids were assayed in exponentially growing and G1‐arrested temperature‐sensitive cell division cycle (cdc) mutants of Saccharomyces cerevisiae. It was observed that cdc28 cells which are known to arrest at ‘start’ when shifted to their non‐permissive temperature, resulted in a 40% decrease in phosphatidylinositol (PI) level while the phosphatidylserine (PS) content was doubled in these cells. The reduced level of PI was restored in cdc4 and cdc7 mutants which are known to arrest past the ‘start’. The increase in PS level in cdc8 mutant which was probably to compensate the intrinsic charging of membrane environment, was also reduced in cdc4 and cdc7 mutants. Our results demonstrate that PI may play a role in yeast cell division and growth that the abnormalities of cdc28 could also be related to PI decrease.