PECULIARITIES OF HEXOSE TRANSPORT AND CATABOLITE REPRESSON REGULATION DY HEXOSE SENSORS HpGcr1 AND HpHxs1 IN THE YEAST HANSENULA POLYMORPHA

Abstract

In the yeasts, as in the majority of microorganisms, glucose is the main source of carbon and energy, as well as a key effector molecule involved in transcriptional regulation. Many genes are repressed in the presence of glucose, others are instead induced by glucose. In the mutants of bakers’ yeast Sacharomyces cerevisiae impaired in hexo­se transport, the proficiency of transport determins the strength of the repression signal. In the mutants of methylotrophic yeast Hansenula polymorpha with deleted glucose sensors НрGcr1 and НрHxs1, efficiency of glucose and fructose uptake and the effect of hexose transport on catabolite repression of peroxisomal alcohol oxidase was investigated. Contrary to S. cerevisiae, in the mutants ∆gcr1 and ∆hxs1 impairment glucose and fructose transport did not always corelated with the rate of catabolite repression of metabolic genes of alternative carbon sources. For instance, in the recessive gcr1-2 mutant with one amino acid substitution S85F glucose transport was less impaired relative to corresponding deletion mutant, whereas defect of glucose repression was more pronounced. Also, in the mutants ∆hxs1 and ∆gcr1, the defect of fructose transport was similar, when fructose repression defect was stronger in ∆hxs1. Therefore, specific impairment of hexose transport upon deletion of alternative hexose sensors in H. polymorpha is not an only cause that determins profiociency of hexose catabolite repression.