title: Nucleotide sequence of the thymidylate synthase B and dihydrofolate reductase genes contained in one Bacillus subtilis operon.
abstract: The nucleotide sequence of the thymidylate synthase B (thyB) and dihydrofolate reductase (dfrA) gene regions from wild-type and trimethoprim-resistant (TpR) mutant strains of Bacillus subtilis 168 was determined. The sequenced region contains two open reading frames, ORF1 and ORF2, which correspond to thyB and dfrA, respectively, and overlap by one nucleotide. The thyB-dfrA genes encode 267 and 168 amino acid polypeptides, respectively, and are present in the order of thyB - dfrA in 5'----3' orientation. This gene order differs from those which have been found in other organisms so far. S1 mapping analysis indicated that both genes were transcribed from a single promoter located upstream from the thyB gene. Thus, the genes belong to an operon. A nucleotide substitution from 'A' in the wild type to 'C' in the TpR mutant was located in the dfrA gene region, with predicted conversion of isoleucine-95 (wild type) to leucine-95 (mutant) in dihydrofolate reductase (DHFR). It is suggested that the affinity between DHFR and Tp is reduced by this alteration.
authors.affiliation: Research Institute for Polymers and Textiles, Ibaraki, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Iwakura
authors.forename: M
authors.initials: M
authors.lastname: Kawata
authors.forename: K
authors.initials: K
authors.lastname: Tsuda
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D002872:Chromosome Deletion; D004262:DNA Restriction Enzymes; D004926:Escherichia coli / Q000235:genetics; D005796:Genes; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009876:Operon; D010957:Plasmids; D012689:Sequence Homology, Nucleic Acid; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D013940:Thymidylate Synthase / Q000235:genetics*
chemical_list: D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; D004262:DNA Restriction Enzymes