Homing events in the gyrA gene of some mycobacteria.
The A subunit of DNA gyrase in Mycobacterium leprae, unlike its counterpart in Mycobacterium tuberculosis, is produced by protein splicing as its gene, gyrA, harbors a 1260-bp in-frame insertion encoding an intein, a putative homing endonuclease. Analysis of the gyrA locus from different mycobacterial species revealed the presence of inteins in Mycobacterium flavescens, Mycobacterium gordonae and Mycobacterium kansasii but not in 10 other pathogenic or saprophytic mycobacteria. In all four cases where intein coding sequences were found, they were localized in the same position in gyrA, immediately downstream of the codon for the key active-site residue Tyr-130. The intein products were similar, but not identical, in sequence and the splice junctions displayed all the features found in other polypeptides known to be produced by protein splicing from a precursor protein. Paired motifs, found in homing endonucleases encoded by some group I RNA introns, and inteins showing endonuclease activity, were present in the gyrA inteins as were other intein-specific signatures. Some strains of M. flavescens, M. gordonae, and M. kansasii were shown by PCR analysis to have inteinless gyrA genes, in contrast to the situation in M. leprae where all the isolates possessed insertions in gyrA. Sequencing of the corresponding regions revealed that, although the GyrA protein sequence was conserved, the nucleotide sequences differed in gyrA genes with and without inteins, suggesting that the homing endonuclease displays sequence specificity.
Fsihi
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Unite de Genetique Moleculaire Bacterienne, Institut Pasteur, Paris, France.
Vincent
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Cole
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D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D027081:DNA Gyrase; D017931:DNA Primers / Q000235:genetics; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D004274:DNA, Recombinant; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000201:enzymology* / Q000235:genetics*; D009166:Mycobacterium leprae / Q000201:enzymology / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000235:genetics; D009170:Nontuberculous Mycobacteria / Q000201:enzymology / Q000235:genetics; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
D017931:DNA Primers; D004269:DNA, Bacterial; D004274:DNA, Recombinant; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II