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Cloning and characterization of the thymidylate synthase gene from Lactococcus lactis subsp. lactis.

ABSTRACT: The thymidylate synthase (thyA) gene has been isolated from Lactococcus lactis subsp. lactis. The cloned gene was strongly expressed in Escherichia coli both in vivo and in vitro (maxicells and cell-free transcription and translation systems) and complemented E. coli thyA mutants. DNA-DNA hybridizations demonstrated that the thyA gene is encoded by the chromosome of L. lactis subsp. lactis. By sequential deletion of DNA outside the complementing region, the thyA gene was localized to a 1.1-kilobase DNA fragment. The nucleotide sequence of the lactococcal thyA gene was determined by the dideoxy-chain termination technique. The derived amino acid sequence indicated a protein size of 32,580 daltons, which is in good agreement with results obtained from maxicell and in vitro transcription and translation experiments. The primary sequence is homologous to 12 other thyA proteins from a variety of other organisms. Upstream from the structural gene, -10 and -35 promoter sequences which were almost canonical sigma-70 promoter sequences were identified, which may explain the strong expression of the thyA gene observed in E. coli. An A-T-rich sequence characteristic of gram-positive promoters was also noted adjacent to the -35 region. The thyA gene has potential as a marker for plasmid maintenance and selection in food systems.

SUBMITTER: Ross P

PROVIDER: S-EPMC184576 | biostudies-other | 1990 Jul

REPOSITORIES: biostudies-other

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Cloning and characterization of the thymidylate synthase gene from Lactococcus lactis subsp. lactis.

Ross P P O'Gara F F Condon S S

Applied and environmental microbiology 19900701 7

The thymidylate synthase (thyA) gene has been isolated from Lactococcus lactis subsp. lactis. The cloned gene was strongly expressed in Escherichia coli both in vivo and in vitro (maxicells and cell-free transcription and translation systems) and complemented E. coli thyA mutants. DNA-DNA hybridizations demonstrated that the thyA gene is encoded by the chromosome of L. lactis subsp. lactis. By sequential deletion of DNA outside the complementing region, the thyA gene was localized to a 1.1-kilob ...[more]

PMID: 2117882

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Project description:A phage-resistant mutant with a defect in a membrane component required for phage infections in Lactococcus lactis subsp. lactis C2 was transformed with a chromosomal library of the wild-type, phage-sensitive strain. Of the 4,200 transformants screened for phage sensitivity, three were positively identified as phage sensitive. A cause-and-effect relationship between the cloned chromosomal fragments and the phage-sensitive phenotype was established on the basis of the following two criteria: (i) the frequency of loss of the cloned fragments in the absence of antibiotic selection pressure correlated with the frequency of loss of phage sensitivity; and (ii) phage sensitivity was transferred to 100% of recipient, phage-resistant cells transformed with the cloned fragment. The cloned chromosomal DNA from the three independent isolates was physically mapped with restriction endonucleases. The sizes of the cloned fragments were 9.6, 11.8, and 9.5 kb. Each fragment contained an identical stretch of DNA common to all three, which was 9.4 kb. The gene that conferred phage sensitivity was localized by subcloning to a 4.5-kb region. Further subcloning indicated that a single EcoRI site within the 4.5-kb region must lie within the gene or its promoter. The required 4.5-kb region was sequenced and found to code for one partial and two complete open reading frames. The gene required for complementation was functionally mapped by Tn5 mutagenesis and localized to one of the two complete open reading frames, which was designated pip (an acronym for phage infection protein). pip is 2,703 bases in length. Potential promoters start 206 and 212 bases upstream of the open reading frame. A ribosome binding site and a seven-base spacer precede the GTG (Val) translation initiation codon. The amino acid sequence deduced from the gene has 901 residues and an M(r) of 99,426. Hydropathy analysis revealed four to six potential membrane-spanning regions, one near the amino terminus and the others at the extreme carboxyl terminus. The amino terminus has characteristics of a signal sequence. The putative protein would have a 650-residue, central polar domain.

Dataset Information

Cloning and characterization of the thymidylate synthase gene from Lactococcus lactis subsp. lactis.

Publications

Cloning and characterization of the thymidylate synthase gene from Lactococcus lactis subsp. lactis.

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