title: [Selection and mutant properties of Pichia guilliermondii yeasts with derepressed GTP cyclohydrolase, the enzyme of the 1st step in flavinogenesis].
abstract: A positive method is proposed for selecting Pichia guilliermondii mutants with derepressed GTP cyclohydrolase. Mutants with the incompletely blocked gene RIB2 were used as parent strains; these can grow in a medium without riboflavin (RF) only if the enzyme is derepressed as the result of iron deficiency in cells. Strains growing in a medium without RF at the optimal supply of cells with iron were selected as regulatory mutants. The mutants accumulated 6,7-dimethylpterin in high concentrations and a small amount of RF in the medium and in the cells. The activity of GTP cyclohydrolase rather than that of RF synthase increased in the mutants; the activity of RF kinase and FAD pyrophosphorylase was not elevated. Hybrids produced by crossing the regulatory mutants with wild type strains did not accumulate 6,7-dimethylpterin in the medium and the activity of the GTP cyclohydrolase did not increase; this is indicative of the negative regulation for the expression of the structural gene for GTP cyclohydrolase. The authors propose a model for the regulation of GTP cyclohydrolase and RF synthase at the gene level involving iron ions as a corepressor.
mesh_terms: D000619:Aminohydrolases / Q000235:genetics*; D001203:Ascomycota / Q000235:genetics*; D005415:Flavins / Q000096:biosynthesis*; D006136:GTP Cyclohydrolase / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D005796:Genes; D009154:Mutation; D009713:Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D010843:Pichia / Q000201:enzymology / Q000235:genetics*; D012258:Riboflavin Synthase / Q000235:genetics / Q000378:metabolism; D012641:Selection, Genetic
chemical_list: D005415:Flavins; D012258:Riboflavin Synthase; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C022532:riboflavin kinase; D009713:Nucleotidyltransferases; C020143:FMN adenylyltransferase; D000619:Aminohydrolases; D006136:GTP Cyclohydrolase
vernacular_title: Selektsiia i svoĭstva mutantov drozhzheĭ Pichia guilliermondii s derepressirovannym fermentom pervogo ĕtapa flavinogeneza--GTF-tsiklogidrolazoĭ.