SFP1 is involved in cell size modulation in respiro-fermentative growth conditions

Saccharomyces cerevisiae grows fast on glucose, while growth slows down on ethanol as cells move from glucose fermentation to oxidative metabolism. The type of carbon source influences both the specific growth rate and cell cycle progression, as well as cell size. Yeast cells grown on glucose have a larger size than cells grown on ethanol. Here, we analysed the behaviour of a sfp1 null mutant during balanced and transitory states of growth in batch in response to changes in the growth medium carbon sources. In a screening for mutants affected in cell size at Start, SFP1 has been identified as a gene whose deletion caused one of the smallest whi phenotype. Findings presented in this work indicate that in the sfp1 null mutant the reduction in cell size is not only a consequence of the reduced growth rate but it is tightly linked to the cellular metabolism. The SFP1 gene product is required to sustain the increase of both rRNA and protein content that in wild-type cells takes place in respiro-fermentative growth conditions, while it seems dispensable for growth on non-fermentable carbon sources. It follows that sfp1 cells growing on ethanol have a larger size than cells growing on glucose and, noticeably, the former enter the S phase with a critical cell size higher than the latter. These features, combined with the role of Sfp1p as a transcriptional factor, suggest that Sfp1p could be an important element in the control of the cell size modulated by nutrients.