title: A high-frequency mutation in Bacillus subtilis: requirements for the decryptification of the gudB glutamate dehydrogenase gene.
abstract: Common laboratory strains of Bacillus subtilis encode two glutamate dehydrogenases: the enzymatically active protein RocG and the cryptic enzyme GudB that is inactive due to a duplication of three amino acids in its active center. The inactivation of the rocG gene results in poor growth of the bacteria on complex media due to the accumulation of toxic intermediates. Therefore, rocG mutants readily acquire suppressor mutations that decryptify the gudB gene. This decryptification occurs by a precise deletion of one part of the 9-bp direct repeat that causes the amino acid duplication. This mutation occurs at the extremely high frequency of 10(-4). Mutations affecting the integrity of the direct repeat result in a strong reduction of the mutation frequency; however, the actual sequence of the repeat is not essential. The mutation frequency of gudB was not affected by the position of the gene on the chromosome. When the direct repeat was placed in the completely different context of an artificial promoter, the precise deletion of one part of the repeat was also observed, but the mutation frequency was reduced by 3 orders of magnitude. Thus, transcription of the gudB gene seems to be essential for the high frequency of the appearance of the gudB1 mutation. This idea is supported by the finding that the transcription-repair coupling factor Mfd is required for the decryptification of gudB. The Mfd-mediated coupling of transcription to mutagenesis might be a built-in precaution that facilitates the accumulation of mutations preferentially in transcribed genes.
authors.affiliation: Department of General Microbiology, Georg-August-University Göttingen, Göttingen, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Gunka
authors.forename: Stefan
authors.initials: S
authors.lastname: Tholen
authors.forename: Jan
authors.initials: J
authors.lastname: Gerwig
authors.forename: Christina
authors.initials: C
authors.lastname: Herzberg
authors.forename: Jörg
authors.initials: J
authors.lastname: Stülke
authors.forename: Fabian M
authors.initials: FM
authors.lastname: Commichau
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D005969:Glutamate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011544:Pseudogenes; D012091:Repetitive Sequences, Nucleic Acid; D013489:Suppression, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D014157:Transcription Factors; C072103:transcription repair coupling factor protein, Bacteria; D005969:Glutamate Dehydrogenase