The Mycoplasma gallisepticum virulence factor lipoprotein MslA is a novel polynucleotide binding protein.

Although lipoproteins of mycoplasmas are thought to play a crucial role in interactions with their hosts, very few have had their biochemical function defined. The gene encoding the lipoprotein MslA in Mycoplasma gallisepticum has recently been shown to be required for virulence, but the biochemical function of this gene is not known. Although this gene has no significant sequence similarity to any gene of known function, it is located within an operon in M. gallisepticum that contains a homolog of a gene previously shown to be a nonspecific exonuclease. We mutagenized both genes to facilitate expression in Escherichia coli and then examined the functions of the recombinant proteins. The capacity of MslA to bind polynucleotides was examined, and we found that the protein bound single- and double-stranded DNA, as well as single-stranded RNA, with a predicted binding site of greater than 1 nucleotide but less than or equal to 5 nucleotides in length. Recombinant MslA cleaved into two fragments in vitro, both of which were able to bind oligonucleotides. These findings suggest that the role of MslA may be to act in concert with the lipoprotein nuclease to generate nucleotides for transport into the mycoplasma cell, as the remaining genes in the operon are predicted to encode an ABC transporter.

Molecular characterization of newly identified IS3, IS4 and IS30 insertion sequence-like elements in Mycoplasma bovis and their possible roles in genome plasticity.

Insertion sequences (ISs) are mobile genetic elements widely distributed among bacteria. Their impact on the bacterial genome is multifold, including transfer of genetic information, shuttle of adaptive traits and influence on the genomic content. As a result, ISs play an important role in the organization, plasticity and evolution of bacterial genomes. In this study, four new IS elements: ISMbov7; ISMbov4 and ISMbov5; and ISMbov6, related, respectively, to the IS3, IS4 and IS30 gene families, were identified and characterized with respect to inverted repeat (IR) and directly repeated (DR) sequences, putative target specificity and motifs related to transposase function. For instance, IS30-related ISMbov6 isoform elements were shown to (1) contain an alpha-helix-turn-alpha-helix homeodomain (HTH), (2) generate long DR and (3) possess target specificity for a palindromic sequence derived from putative rho-independent transcription terminators. Members of the IS3 family, which had not been documented previously in Mycoplasma bovis, contain HTH, leucine zipper and AT-hook motifs, which may be involved in DNA binding. In addition, the availability of the M. bovis PG45 genome sequence allowed us to elucidate the genomic organization of 54 intact or truncated IS elements and their possible effect on the expression of adjacent genes.