REGULATION OF GENES ENCODING SUBUNITS OF THE TREHALOSE SYNTHASE COMPLEX IN SACCHAROMYCES-CEREVISIAE - NOVEL VARIATIONS OF STRE-MEDIATED TRANSCRIPTION CONTROL

Saccharomyces cerevisiae cells show under suboptimal growth conditions a complex response that leads to the acquisition of tolerance to diff erent types of environmental stress. This response is characterised by enhanced expression of a number of genes which contain so-called stre ss-responsive elements (STREs) in their promoters. In addition, the ce lls accumulate under suboptimal conditions the putative stress protect ant trehalose. in this work, we have examined the expression of four g enes encoding subunits of the trehalose synthase complex, GGS1/TPS1, T PS2, TPS3 and TSL1. We show that expression of these genes is coregula ted under stress conditions. Like for many other genes containing STRE s, expression of the trehalose synthase genes is also induced by heat and osmotic stress and by nutrient starvation, and negatively regulate d by the Ras-cAMP pathway. However, during fermentative growth only TS L1 shows an expression pattern like that of the STRE-controlled genes CTT1 and SSA3, while expression of the three other trehalose synthase genes is only transiently down-regulated. This difference in expressio n might be related to the known requirement of trehalose biosynthesis for the control of yeast glycolysis and hence for fermentative growth. We conclude that the mere presence in the promoter of (an) active STR E(s) does not necessarily imply complete coregulation of expression, A dditional mechanisms appear to fine tune the activity of STREs in orde r to adapt the expression of the downstream genes to specific requirem ents.