Cell size is regulated by phospholipids and not by storage lipids in Saccharomyces cerevisiae.

Cell size and morphology are key adaptive features that influence almost all aspects of cellular physiology such as cell cycle and lipid metabolism. Here we report the role of a transcription factor Suppressor Phenotype of Ty elements insertion 10 (SPT10) of Saccharomyces cerevisiae in regulating cell cycle, cell size and lipid metabolism in concert, in addition to its defined role of histone gene expression. Morphological and biochemical analyses of spt10Δ strain show an abnormal cell size, cell cycle and lipid levels. The expression of Spt10p in spt10Δ strain helps the cell revert to typical wild-type phenotypes. SPT10 controls lipid metabolism by negatively regulating the expression of lipid biosynthetic genes, and positively regulating the expression of the lipid hydrolyzing genes. Spt10p helps in maintaining the cell size by regulating the amount of carbon flux into the phospholipid constituents of the cell membranes. On the contrary, storage lipids have no role in regulating the cell size. An exogenous supply of phosphatidic acid increases the cell size, proving the positive impact of the phospholipids on cell size modulation. SPT10 affects cell cycle, cell size and lipid metabolism by an orchestrated transcriptional regulation of the corresponding genes.