title: Glutamine synthetase sequence evolution in the mycobacteria and their use as molecular markers for Actinobacteria speciation.
abstract: BACKGROUND
  Although the gene encoding for glutamine synthetase (glnA) is essential in several organisms, multiple glnA copies have been identified in bacterial genomes such as those of the phylum Actinobacteria, notably the mycobacterial species. Intriguingly, previous reports have shown that only one copy (glnA1) is essential for growth in M. tuberculosis, while the other copies (glnA2, glnA3 and glnA4) are not.
  
  
  RESULTS
  In this report it is shown that the glnA1 and glnA2 encoded glutamine synthetase sequences were inherited from an Actinobacteria ancestor, while the glnA4 and glnA3 encoded GS sequences were sequentially acquired during Actinobacteria speciation. The glutamine synthetase sequences encoded by glnA4 and glnA3 are undergoing reductive evolution in the mycobacteria, whilst those encoded by glnA1 and glnA2 are more conserved.
  
  
  CONCLUSIONS
  Different selective pressures by the ecological niche that the organisms occupy may influence the sequence evolution of glnA1 and glnA2 and thereby affecting phylogenies based on the protein sequences they encode. The findings in this report may impact the use of similar sequences as molecular markers, as well as shed some light on the evolution of glutamine synthetase in the mycobacteria.
authors.affiliation: DST/NRF Centre for Excellence in Biomedical Tuberculosis Research, US/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Faculty of Health Sciences - Stellenbosch University, South Africa. dh@sun.ac.za
authors.forename: Don
authors.initials: D
authors.lastname: Hayward
authors.forename: Paul D
authors.initials: PD
authors.lastname: van Helden
authors.forename: Ian J F
authors.initials: IJ
authors.lastname: Wiid
mesh_terms: D039903:Actinobacteria / Q000235:genetics*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D017124:Conserved Sequence; D004269:DNA, Bacterial / Q000235:genetics; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005819:Genetic Markers; D049810:Genetic Speciation; D016680:Genome, Bacterial; D005974:Glutamate-Ammonia Ligase / Q000235:genetics*; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000235:genetics; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D005819:Genetic Markers; D012336:RNA, Ribosomal, 16S; D005974:Glutamate-Ammonia Ligase