Gene Rearrangements in the vsa Locus of Mycoplasma pulmonis

Abstract

The vsa genes of Mycoplasma pulmonis encode the V-1 lipoproteins. Most V-1 proteins contain repetitive domains and are thought to be involved in mycoplasma-host cell interactions. Previously, we have reported the isolation and characterization of six vsa genes comprising a 10-kb region of the genome of M. pulmonis strain KD735-15. In the current study, vsa-specific probes were used to clone several fragments from a genomic library of KD735-15 DNA and assemble a single 20-kb contig containing 11 vsa genes. The middle region of the vsa locus contains a large open reading frame (ORF) that is not a vsa gene and has undergone an internal deletion in some strains. The ORF is predicted to encode a membrane protein that may have a role in disease pathogenesis. To examine vsa genes in a strain of M. pulmonis that is unrelated to KD735-15, strain CT was studied. Through Southern hybridization and genomic cloning analyses, CT was found to possess homologs of the KD735-15 vsaA, -C, -E, and -F genes and two unique genes (vsaG and vsaH) that were not found in KD735-15. High-frequency, site-specific DNA inversions serve to regulate the phase-variable production of individual V-1 proteins. As a result of the sequence analysis of vsa recombination products, a model in which DNA inversion arises from strand exchange involving at least six nucleotides of the vrs box is proposed.Mycoplasmas cause slowly progressive, chronic diseases in human and animals. The mechanisms of mycoplasmal disease pathogenesis are poorly understood, and there are no effective control measures. Mycoplasma pulmonis is the etiologic agent of murine respiratory mycoplasmosis and can also cause genital disease and arthritis in rats and mice (31). Thus, M. pulmonis can colonize a variety of epithelial surfaces. Rat isolates of M. pulmonis such as strains UAB 5782 and UAB 6510 are generally more virulent in rats than in mice (10,11,24). In the mouse, UAB 5782 and UAB 6510 colonize the respiratory tract without usually causing lesions (10). In contrast, the mouse isolate strain CT causes severe respiratory disease in the mouse (6,7,10,12). Mycoplasma factors that contribute to the host specificity of disease are unknown. A comparison of the proteins produced by 18 strains of M. pulmonis revealed mostly conserved proteins that were invariant among strains (38). An exception was the V-1 family of surface proteins that are encoded by the vsa (variable surface antigen) genes (4,21,33,35,39). Variation in the V-1 proteins may contribute to the host specificity of the mycoplasma and to the chronicity and severity of disease.The chronic nature of mycoplasmal diseases indicates that mycoplasmas can adapt to the rapidly changing conditions in the host. Previous studies had shown that phenotypic variation and genetic recombination occur at high frequencies in M. pulmonis (3). The vsa genes comprise one of the highly recombinogenic loci in this species. Recombination between vsa genes involves site-specific DNA inversions occurring at a 34-bp sequence that defines the vsa ...

Variability of a glucose phosphotransferase system permease in Mycoplasma mycoides subsp. mycoides Small Colony

“…Variable proteins are often subjected to both size and phase variation, and many are members of multigene families. The proteins of a multigene family are often differentially expressed, and chromosomal rearrangements occur to allow transcription of one gene instead of another (Lysnyansky et al, 1999;Citti et al, 2000;Markham et al, 1994Markham et al, , 1999 FlitmanTene et al, 2000; Glew et al, 2000; Roske et al, 2001;Shen et al, 2000;Horino et al, 2003;Noormohammadi et al, 1998).…”

“…Variable proteins are often subjected to both size and phase variation, and many are members of multigene families. The proteins of a multigene family are often differentially expressed, and chromosomal rearrangements occur to allow transcription of one gene instead of another (Lysnyansky et al, 1999;Citti et al, 2000;Markham et al, 1994Markham et al, , 1999 FlitmanTene et al, 2000; Glew et al, 2000; Roske et al, 2001;Shen et al, 2000;Horino et al, 2003;Noormohammadi et al, 1998).Mmymy SC was originally thought not to exhibit intraclonal variability, but a variable surface protein Vmm (Persson et al, 2002) that undergoes reversible phase variation has recently been identified. The vmm gene has been demonstrated in all Mmymy SC strains as a single copy and is regulated at the transcriptional level by dinucleotide (AT) insertions or deletions in a repetitive region of the promoter spacer.…”

The Complete Genome and Proteome of Mycoplasma mobile

“…For example, M. pulmonis has the vsa proteins and M. pneumoniae has the P1 protein present many times each in the genome (Himmelreich et al 1996;Chambaud et al 2001). In the case of M. pulmonis, a promoter sequence is moved from copy to copy of vsa to effect antigenic switching (Bhugra et al 1995;Shen et al 2000). In M. pneumoniae, it is believed that homologous recombination transfers different variants of the P1 gene into an actively transcribed locus (Kenri et al 1999).…”

Surface Diversity in Mycoplasma agalactiae Is Driven by Site-Specific DNA Inversions within the vpma Multigene Locus

“…DNA rearrangements associated with changes in gene expression have also been found for Vsps (20,22). Two other well-described systems involving DNA rearrangements in mycoplasmas are the vsa and hsd systems in M. pulmonis (5,35,37,38). Both systems generate variation in expression of a given product by exchanging the C-terminal region of the active gene with the open reading frame (ORF)…”