title: Effects of regulatory mutations upon methionine biosynthesis in Saccharomyces cerevisiae: loci eth2-eth3-eth10.
abstract: The effects of mutations occurring at three independent loci, eth2, eth3, and eth10, were studied on the basis of several criteria: level of resistance towards two methionine analogues (ethionine and selenomethionine), pool sizes of free methionine and S-adenosyl methionine (SAM) under different growth conditions, and susceptibility towards methionine-mediated repression and SAM-mediated repression of some enzymes involved in methionine biosynthesis (met group I enzymes). It was shown that: (i) the level of resistance towards both methionine analogues roughly correlates with the amount of methionine accumulated in the pool; (ii) the repressibility of met group I enzymes by exogenous methionine is either abolished or greatly lowered, depending upon the mutation studied; (iii) the repressibility of the same enzymes by exogenous SAM remains, in at least three mutants studied, close to that observed in a wild-type strain; (iv) the accumulation of SAM does not occur in the most extreme mutants either from endogenously overproduced or from exogenously supplied methionine: (v) the two methionine-activating enzymes, methionyl-transfer ribonucleic acid (tRNA) synthetase and methionine adenosyl transferase, do not seem modified in any of the mutants presented here; and (vi) the amount of tRNA(met) and its level of charging are alike in all strains. Thus, the three recessive mutations presented here affect methionine-mediated repression, both at the level of overall methionine biosynthesis which results in its accumulation in the pool, and at the level of the synthesis of met group I enzymes. The implications of these findings are discussed.
mesh_terms: D000255:Adenosine Triphosphate; D001554:Benzene / Q000494:pharmacology; D002474:Cell-Free System; D004794:Enzyme Repression; D005001:Ethionine / Q000494:pharmacology; D005796:Genes; D006710:Homocysteine; D008715:Methionine / Q000096:biosynthesis* / Q000494:pharmacology; D008780:Methyltransferases / Q000096:biosynthesis; D009154:Mutation; D009713:Nucleotidyltransferases / Q000096:biosynthesis; D010088:Oxidoreductases / Q000096:biosynthesis; D012436:S-Adenosylmethionine / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D013237:Stereoisomerism; D013447:Sulfites; D014166:Transferases / Q000096:biosynthesis
chemical_list: D013447:Sulfites; D006710:Homocysteine; D012436:S-Adenosylmethionine; D000255:Adenosine Triphosphate; D008715:Methionine; D010088:Oxidoreductases; D014166:Transferases; D008780:Methyltransferases; D009713:Nucleotidyltransferases; D001554:Benzene; D005001:Ethionine