Production of the STA2‐encoded glucoamylase in Saccharomyces cerevisiae is subject to feed‐back control

Abstract

Three modes of production of the extracellular glucoamylase (GA) in Saccharomyces cerevisiae have been identified; repressed, basal and induced. The repressed mode is found with cells grown in rich media containing non-limiting concentrations of monosaccharides or disaccharides, including GA-hydrolysable maltose, as a sole carbon source. Both the basal and the induced modes (spanned by some seven-fold differences in the rate of GA production) can be displayed by either glucose-limited or glycerol-plus ethanol-consuming cultures; the induced mode is switched over to the basal one due to a feed-back inhibition by extracellularly accumulated GA. It is proposed that the feed-back control involved in GA production can be attenuated by starch which can thus 'induce' higher rates of GA production compared to the basal mode.

Divergent Regulation of the Evolutionarily Closely Related Promoters of the Saccharomyces cerevisiae STA2 and MUC1 Genes

“…These data are in good agreement with previous reports on the transcriptional activity of either STA2 or MUC1, determined by Northern blot analysis. Transcription of MUC1 was reported to be repressed in rich medium (27,28,44) or medium containing glucose as the carbon source (8), whereas STA1 and STA2 were reported to be repressed in all media containing readily metabolized carbon sources such as glucose (5,8,17,20,41,47).…”

“…Expression of STA1 to -3 is negatively regulated at several levels. Transcription is repressed on most readily metabolized carbon sources, including glucose, sucrose, maltose, and galactose (5,17,20,41,47). Carbon catabolite repression was reported to involve two separate pathways, of which one requires HXK2 and the other HAP2 (17).…”

Genes required for derepression of an extracellular glucoamylase gene, STA2, in the yeast Saccharomyces

“…Meanwhile, in our previous experiments we found no detectable GA activity to be accumulated by exponential-phase cultures of an STA2 strain, YBS249, growing on glucose (Suntsov et al, 1991). Although some derepression of GA synthesis occurred upon glucose exhaustion, the stationary-phase GA accumulation level was still eightfold lower than that observed in the use of non-fermentable carbon sources.…”

“…YP medium (Suntsov et al, 1991) was supplemented with: 2% glucose (YPD), 0.05% glucose (YPd), 3% glycerol (YPG), 2% ethanol (YPE), 3% glycerol plus 2% ethanol (YPGE), 2% starch (YPS), 2% starch plus 3% glycerol plus 2% ethanol (YPSGE).…”

“…GA activity (Sta phenotype) was assayed in two ways: (a) qualitative assays were conducted on YPSGE agar plates; cells were grown for 2 4 days at 28"C, and the plates were then incubated at 4°C overnight to precipitate undegraded starch; clear starch degradation haloes could thus be visualized around Sta' clones; Sta-clones formed no haloes; (b) quantitative assays were conducted essentially as previously described (Suntsov et al, 1991), except that starch ( I YO, w/v, final concentration) was used as the substrate; prior to being assayed, the cell-free culture liquid probes were dialysed extensively against 100 mM-phosphate buffer, pH 5.4; the GA units were expressed as nmol of glucose released from starch/min. Acid phosphatase activity (Pho phenotype) was assayed on YPD agar plates using a qualitative overlay procedure.…”