EXPRESSION OF GENES OF PUTATIVE HEXOSE TRANSPORTERS IN THE YEAST HANSENULA POLYMORPHA ARE DIFFERENTIALLY REGULATED BY GLUCOSE SENSORS Hxs1 AND Gcr1

Abstract

The first and limiting step of metabolism of glucose, the most widespread carbon and energy source for majority of cells, is the transport of this sugar across cytoplasmic membrane. In the eukaryotic cells glucose controls and ensures its own effective metabolism, acting as extracellular effector, regulating on transcriptional and translational levels amount, type and activity of corresponding hexose transporters. In this study we investigated regulation of expression of genes encoding hexose transporter homologues – НрHxt1, НрHxt2, НрHxt3 and putative fructose transporter – НрFrt1 by two glucose sensors НрGcr1 and НрHxs1 in methylotrophic yeast Hansenula polymorpha. We have demonstrated that putative glucose sensor НрGcr1 is involved in repression of the gene of functional low affinity hexose transporter НрHxt1 under glucose deficient conditions and participates in repression of genes of putative high affinity glucose transporters НрHxt2 and НрHxt3 under excess of this carbon source. It was shown that glucose sensor НрHxs1 is involved in induction of НрHxt1 expression. As a result of deletion of HpGCR1, but not НрHxS1, the gene of putative high affinity fructose transporter НрFRT1 is constitutively expressed independently of glucose pre­sence and its concentration in growth medium. Therefore, regulation of hexose (glucose and fructose) transport in methylotrophic yeast H. polymorpha at the level of gene expression is a complicated system of interac­ting regulatory and transporting elements where glucose sensors НрGcr1 and НрHxs1 act as the key factors.