RESUMO
In response to an external source of adenine, yeast cells repress the expression of purine biosynthesis pathway genes. To identify necessary components of this signalling mechanism, we have isolated mutants that are constitutively active for expression. These mutants were named bra (for bypass of repression by adenine). BRA7 is allelic to FCY2, the gene encoding the purine cytosine permease and BRA9 is ADE12, the gene encoding adenylosuccinate synthetase. BRA6 and BRA1 are new genes encoding, respectively, hypoxanthine guanine phosphoribosyl transferase and adenylosuccinate lyase. These results indicate that uptake and salvage of adenine are important steps in regulating expression of purine biosynthetic genes. We have also shown that two other salvage enzymes, adenine phosphoribosyl transferase and adenine deaminase, are involved in activating the pathway. Finally, using mutant strains affected in AMP kinase or ribonucleotide reductase activities, we have shown that AMP needs to be phosphorylated to ADP to exert its regulatory role while reduction of ADP into dADP by ribonucleotide reductase is not required for adenine repression. Together these data suggest that ADP or a derivative of ADP is the effector molecule in the signal transduction pathway.
Assuntos
Adenina/biossíntese , Genes Fúngicos , Mutação , Saccharomyces cerevisiae/genética , Adenina/metabolismo , Difosfato de Adenosina/análogos & derivados , Difosfato de Adenosina/biossíntese , Adenilossuccinato Liase/química , Adenilossuccinato Liase/genética , Sequência de Aminoácidos , Teste de Complementação Genética , Hipoxantina Fosforribosiltransferase/química , Hipoxantina Fosforribosiltransferase/genética , Dados de Sequência Molecular , Fenótipo , Saccharomyces cerevisiae/isolamento & purificação , Homologia de Sequência de Aminoácidos , Transdução de SinaisRESUMO
Base analog 6-N-hydroxylaminopurine is a potent mutagen in variety of prokaryotic and eukaryotic organisms. In the review, we discuss recent results of the studies of HAP mutagenic activity, genetic control and specificity in bacteria and yeast with the emphasis to the mechanisms protecting living cells from mutagenic and toxic effects of this base analog.
Assuntos
Adenina/análogos & derivados , Antimutagênicos/farmacologia , Escherichia coli/efeitos dos fármacos , Mutagênicos/farmacologia , Saccharomyces cerevisiae/efeitos dos fármacos , Adenina/farmacologia , Sequência de Aminoácidos , Sequência de Bases , DNA Bacteriano/efeitos dos fármacos , DNA Fúngico/efeitos dos fármacos , Escherichia coli/genética , Dados de Sequência Molecular , Saccharomyces cerevisiae/genética , Homologia de Sequência de AminoácidosRESUMO
A new Saccharomyces cerevisiae gene, XPT1, was isolated as a multicopy suppressor of a hypoxanthine phosphoribosyl transferase (HPRT) defect. Disruption of XPT1 affects xanthine utilization in vivo and results in a severe reduction of xanthine phosphoribosyl transferase (XPRT) activity while HPRT is unaffected. We conclude that XPT1 encodes XPRT in yeast.
Assuntos
Genes Fúngicos , Pentosiltransferases/genética , Saccharomyces cerevisiae/genética , Xantina/metabolismo , Hipoxantina Fosforribosiltransferase/genética , Purinas/metabolismo , Saccharomyces cerevisiae/enzimologia , Supressão GenéticaRESUMO
The yeast Saccharomyces cerevisiae has two separate genes (APT1 and APT2) that encode two potentially different forms of adenine phosphoribosyltransferase (APRT). However, genetic analysis indicated that only APT1 could code for a complementing activity. Cloning and expression of both the APT1 and APT2 genes in Escherichia coli showed that although discrete proteins (APRT1 and APRT2) were made by these genes, only APRT1 had detectable APRT activity. Northern and Western blot analyses demonstrated that only APT1 was transcribed and translated under normal physiological conditions in yeast. Phylogenetic analysis revealed that APRT1 and APRT2 are evolutionary closely related and that they arise from a gene duplication event. We conclude that APT1 is the functional gene in S. cerevisiae and that APT2 is a pseudogene.