A dominant negative effect of eth-1r, a mutant allele of the Neurospora crassa S-adenosylmethionine synthetase-encoding gene conferring resistance to the methionine toxic analogue ethionine.
eth-1r, a thermosensitive allele of the Neurospora crassa S-adenosylmethionine (AdoMet) synthetase gene that confers ethionine resistance, has been cloned and sequenced. Replacement of an aspartic amino acid residue (D48-->N48), perfectly conserved in prokaryotic, fungal and higher eukaryotic AdoMet synthetases, was found responsible for both thermosensitivity and ethionine resistance conferred by eth-1r. Gene fusion constructs, designed to overexpress eth-1r in vivo, render transformant cells resistant to ethionine. Dominance of ethionine resistance was further demonstrated in eth-1+/eth-1r partial diploids carrying identical gene doses of both alleles. Heterozygous eth-1+/eth-1r cells have, at the same time, both the thermotolerance conferred by eth-1+ and the ethionine-resistant phenotype conferred by eth-1r. AdoMet levels and AdoMet synthetase activities were dramatically decreased in heterozygous eth-1+/ eth-1r cells. We propose that this negative effect exerted by eth-1r results from the in vivo formation of heteromeric eth-1+/eth-1r AdoMet synthetase molecules.
Barra
J L
JL
Departamento de Química Biológica (CIQUIBIC-CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
Mautino
M R
MR
Rosa
A L
AL
D000483:Alleles; D000595:Amino Acid Sequence; D002273:Carcinogens / Q000633:toxicity*; D004352:Drug Resistance, Microbial / Q000235:genetics*; D005001:Ethionine / Q000633:toxicity*; D008715:Methionine / Q000031:analogs & derivatives; D008716:Methionine Adenosyltransferase / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D009492:Neurospora crassa / Q000187:drug effects / Q000235:genetics*
D002273:Carcinogens; D008715:Methionine; D008716:Methionine Adenosyltransferase; D005001:Ethionine