title: Positive selection of mutants defective in transcriptional repression of riboflavin synthesis by iron in the flavinogenic yeast Pichia guilliermondii.
abstract: It is known for many years that iron represses synthesis of riboflavin (RF) and most of RF-synthesizing enzymes in several yeast species, known as flavinogenic yeasts. However, the mechanism of such repression is not known. We have found that iron represses transcription of RIB1 and RIB7 genes coding for the first and the last enzymes of RF biosynthesis in the model flavinogenic organism Pichia guilliermondii. To decipher molecular mechanisms of iron-dependent repression, isolation and study of the regulatory mutants defective in corresponding regulation is desirable. However, no suitable methods for isolation of such mutants were previously available. We have produced a single-point transition mutation in the RIB1 gene. The corresponding rib1-86 mutant exhibits leaky phenotype and is unable to grow in iron-sufficient minimal medium without exogenous RF. However, it can grow in minimal iron-deficient medium without RF, or in iron-sufficient medium upon introduction of the previously-isolated regulatory mutation rib81, which leads to increase in RF production. Using the rib1-86 mutant as parental strain, a collection of mutants able to grow in iron-sufficient medium without exogenous RF has been isolated. The mutants appeared to be defective in regulation of RF biosynthesis and iron homeostasis and were divided into six new complementation groups. Study of one corresponding mutant, red6, showed derepression of RIB1 mRNA synthesis in iron-sufficient medium.
authors.affiliation: Department of Molecular Genetics and Biotechnology Institute of Cell Biology, NAS of Ukraine, Lviv.
authors.forename: Yuriy R
authors.initials: YR
authors.lastname: Boretsky
authors.forename: Kostyantyn Y
authors.initials: KY
authors.lastname: Kapustyak
authors.forename: Lyubov R
authors.initials: LR
authors.lastname: Fayura
authors.forename: Oleh V
authors.initials: OV
authors.lastname: Stasyk
authors.forename: Mykola M
authors.initials: MM
authors.lastname: Stenchuk
authors.forename: Yaroslav P
authors.initials: YP
authors.lastname: Bobak
authors.forename: Lyudmyla B
authors.initials: LB
authors.lastname: Drobot
authors.forename: Andriy A
authors.initials: AA
authors.lastname: Sibirny
mesh_terms: D000595:Amino Acid Sequence; D015152:Blotting, Northern; D004271:DNA, Fungal / Q000235:genetics; D006136:GTP Cyclohydrolase / Q000235:genetics / Q000378:metabolism*; D007501:Iron / Q000494:pharmacology*; D008969:Molecular Sequence Data; D010843:Pichia / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D017354:Point Mutation; D012331:RNA, Fungal / Q000737:chemistry / Q000235:genetics; D012256:Riboflavin / Q000096:biosynthesis*; D012641:Selection, Genetic; D016415:Sequence Alignment; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D004271:DNA, Fungal; D012331:RNA, Fungal; D007501:Iron; D006136:GTP Cyclohydrolase; D012256:Riboflavin