RESUMO
Plants and the fission yeast Schizosaccharomyces pombe synthesize small cadmium-binding peptides, called phytochelatins, in response to cadmium. Derived from glutathione (GSH: gamma-Glu-Cys-Gly), they have the general structure (gamma-Glu-Cys)nGly, where n is 2-11. In order to study the biosynthesis of phytochelatins, we used the mutagen N-methyl-N'-nitro-N nitrosoguanidine (MNNG) to select mutants with a lowered GSH content. GSH-deficient mutants show a Cd-sensitive phenotype, whereas resistance to Cu is only slightly influenced. These Cd-sensitive mutants contain 2-15% of the wild-type GSH level. For three mutants a lowered activity of gamma-glutamylcysteine synthetase was measured. One of the mutants was transformed to Cd-resistance and the complementing fragment was analyzed further. The complementing fragment hybridized with chromosome III. In the transformants, GSH content was restored up to wild-type levels, whereas the activity of gamma-glutamylcysteine synthetase was significantly increased compared with the wild-type. Possible mechanisms for Cd-resistance in the transformants are discussed.
Assuntos
Cádmio/farmacologia , Glutationa/biossíntese , Schizosaccharomyces/efeitos dos fármacos , Cobre/farmacologia , Resistência a Medicamentos , Metaloproteínas/biossíntese , Mutação , Fitoquelatinas , Proteínas de Plantas/biossíntese , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo , Transformação GenéticaRESUMO
By complementation of a mutant resistant to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) we have identified the gcs1 gene, encoding a putative gamma-glutamylcysteine synthetase. The gene is possibly interrupted by two introns and has 49% identical and 80% similar amino acids compared with the homologous protein from rat. In comparison with the Saccharomyces cerevisiae homologue it possesses 41% identical and 74% similar amino acids.
Assuntos
Genes Fúngicos , Glutamato-Cisteína Ligase/genética , Schizosaccharomyces/genética , Sequência de Aminoácidos , Sequência de Bases , Glutamato-Cisteína Ligase/química , Íntrons , Dados de Sequência Molecular , Schizosaccharomyces/enzimologiaRESUMO
The complete nucleotide sequence of Saccharomyces cerevisiae chromosome VII has 572 predicted open reading frames (ORFs), of which 341 are new. No correlation was found between G+C content and gene density along the chromosome, and their variations are random. Of the ORFs, 17% show high similarity to human proteins. Almost half of the ORFs could be classified in functional categories, and there is a slight increase in the number of transcription (7.0%) and translation (5.2%) factors when compared with the complete S. cerevisiae genome. Accurate verification procedures demonstrate that there are less than two errors per 10,000 base pairs in the published sequence.