Identification of regulatory genes of riboflavin permease and α-glucosidase in the yeast Pichia guilliermondii.

The method for a positive selection of Pichia guilliermondii yeast mutants which constitutively synthesize riboflavin (RF) permease has been developed. A genetic analysis revealed two regulatory genes of negative action (RFP80, RFP81) and one gene of positive action (RFP82); mutations in these loci determined the ability to synthesize RF permease in the medium without an inducer (α-glucosides). The constitutive mutants with cold-sensitive products of RFP80 and RFP81 genes were isolated. Interafelic complementation within RFP80 locus as well as restoration of the wild (inducible) phenotype in some hybrids between recessive rfp80 mutants and dominant RFP82 (c) mutants were observed. These data suggest a protein structure of products of identified regulatory loci and a direct interaction of the products of RFP80 and RFP82 genes.A meiotic segregants unable to synthesize RF permease in the inducer-containing media (genotype rfp82) were isolated by means of intragenic recombination in RFP82 locus. Epistasis-hypostasis test showed that gene RFP82 acted after gene RFP80. RFP80, RFP81 and RFP82 loci are involved in regulation of biosynthesis of both RF permease and α-glucosidase. The model for action of RFP80 and RFP82 gene products in the expression of RF permease and α-glucosidase structural genes of P. gulliermondii is presented.