title: The vaa locus of Mycoplasma hominis contains a divergent genetic islet encoding a putative membrane protein.
abstract: BACKGROUND
  The Mycoplasma hominis vaa gene encodes a highly variable, surface antigen involved in the adhesion to host cells. We have analysed the structure of the vaa locus to elucidate the genetic basis for variation of vaa.
  
  
  RESULTS
  Mapping of vaa on existing physical maps of five M. hominis isolates by pulsed field gel electrophoresis revealed that vaa is located in a genomic region containing the majority of other characterized membrane protein genes of M. hominis. Sequencing of an 11 kb region containing the vaa locus of M. hominis isolate 132 showed the presence of conserved housekeeping genes at the borders of the region, uvrA upstream and the hitABL operon downstream to vaa. Analysis of 20 M. hominis isolates revealed that the vaa upstream region was conserved whereas the downstream region was highly variable. In isolate 132 this region contained an open reading frame (ORF) encoding a putative 160 kDa membrane protein. Homologous ORFs were present in half of the isolates, whereas this ORF, termed vmp (variable membrane protein), was deleted from the locus in the remaining isolates. Compellingly, the conserved upstream region and variable downstream region of vaa correlates with the genetic structure of vaa itself which consists of a conserved 5' end and a variable 3' end containing a variable number of exchangeable sequence cassettes.
  
  
  CONCLUSIONS
  Our data demonstrate that the vaa locus contains a divergent genetic islet, and indicate pronounced intraspecies recombination. The high variability level of the locus indicate that it is a chromosomal 'hot spot', presumably important for sustaining diversity and a high adaptation potential of M. hominis.
authors.affiliation: Department of Medical Microbiology and Immunology, University of Aarhus, DK-8000 Aarhus C, Denmark. tboesen@bioxray.dk.
authors.forename: Thomas
authors.initials: T
authors.lastname: Boesen
authors.forename: Jeppe
authors.initials: J
authors.lastname: Emmersen
authors.forename: Agata
authors.initials: A
authors.lastname: Baczynska
authors.forename: Svend
authors.initials: S
authors.lastname: Birkelund
authors.forename: Gunna
authors.initials: G
authors.lastname: Christiansen
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics*; D002874:Chromosome Mapping; D005798:Genes, Bacterial; D014644:Genetic Variation; D008565:Membrane Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D019535:Mycoplasma hominis / Q000235:genetics* / Q000302:isolation & purification; D016366:Open Reading Frames; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
chemical_list: D018829:Adhesins, Bacterial; D008565:Membrane Proteins; C115186:Vaa protein, Mycoplasma hominis