Expression of the pMGA Genes of Mycoplasma gallisepticum Is Controlled by Variation in the GAA Trinucleotide Repeat Lengths within the 5′ Noncoding Regions

Abstract

We analyzed the segment of DNA which contains the expressed pMGA gene from one strain of Mycoplasma gallisepticum in normal (strain S6) cells and in cells in which pMGA1.1 gene expression had ceased as a consequence of in vitro culture in the presence of pMGA1.1-specific antibodies. Sequence analysis of isolates lacking pMGA1.1 expression revealed that this gene, which is typically expressed, exhibited sequence changes within a region 5′ to its promoter. Specifically, pMGA1.1+ cells contained a (GAA)12 motif upstream of the promoter, whereas in pMGA1.1− cells the corresponding region contained a (GAA)10 motif; when such cells were grown in medium no longer containing pMGA-specific antibodies, pMGA1.1 was reexpressed and the 5′ (GAA)12 motif was restored. Two other genes, pMGA1.9 and pMGA1.2, were also shown to acquire a (GAA)12 motif in clones which expressed these genes. The results imply the evolution by the pMGA genes of M. gallisepticum of a novel transcriptional requirement which facilitates rapid and reversible switches in the pMGA expression pattern.

The role of variable DNA tandem repeats in bacterial adaptation

“…This difference in distribution is also reflected in different functional roles. In M. gallisepticum, the most prominent trinucleotide TRs are the GAA repeats in the 5′ untranslated region of the 42 up to 70 vlpA adhesin gene paralogs that exist in each strain, which regulate vlpA gene expression (Glew et al, 1998(Glew et al, , 2000Liu et al, 2000;Papazisi et al, 2003). In contrast, M. hyopneumoniae trinucleotide repeats are found mostly within hypothetical ORFs, but also in some adhesins, and their contraction or expansion results in variability of amino acid repeats that are believed to play a role in protein-protein interaction or adhesion (Mr azek, 2006).…”

Sequence polymorphisms within the pMGA genes and pMGA antigenic variants in Mycoplasma gallisepticum

“…Rabbit polyclonal antibodies pAb t pMGA against truncated recombinant pMGA1.1 (aa residues from 37 to about 300) and rabbit antiserum to pMGA1.9 were also used. Antibodies to pMGA1.9 protein do not react with pMGA1.1 or pMGA1.2 but only with pMGA1.9, which is a 82-kDa polypeptide synthesized in S6 strain [8,15].…”

“…The total RNA was extracted from the Mycoplasma cells grown to the late exponential phase [15] using Trizol 0 reagent (GibcoBRL, Paisley, UK) and used as a template in a reverse transcription (RT) reaction. The ¢rst strand cDNA synthesis was initiated using the PMGA1.R primer and MuLV reverse transcriptase (Perkin Elmer, Foster City, CA, USA), followed by the RT-PCR using either PMGA1.F and PMGA1.R or PMGA2.F and PMGA2.R primers.…”

“…The mAb 66 that reacts with pMGA1.1 and mAbs 71 and 86 that react also with pMGA1.2 were described elsewhere [4,8,15]. The mAb A3 reacts with pMGA1.1 and pMGA1.2 [14,16].…”

“…We expected that the sequence data showing the di¡erences at the 5P-end of the pMGA gene might be useful for strain di¡erentiation. Patterns of pMGA expression and occurrence of antigenically distinct pMGA1.9 protein have been previously investigated only in a highly passaged S6 strain [8,15]. However, we already ¢fth passage [12].…”