Organization of the Mycoplasma synoviae WVU 1853T vlhA gene locus

Mycoplasma synoviae cause respiratory disease and synovitis in poultry. It has two major membrane antigens of approximately 45 to 50 kDa, MSPA and MSPB. Both MSPA and MSPB ar encoded by a single gene, vlhA (variable lipoprotein and haemagglutinin), possibly with a post-translational cleavage generating the two proteins. The vlhA gene belongs to a large multigene family, but only one vlhA gene is expressed in any single cell; the other vlhA genes/fragments are transcriptionally silent. In order to characterize the vlhA gene locus, DNA fragments were cloned from three different M. synoviae WVU 1853(T) genomic DNA libraries and their nucleotide sequences were fully or partially determined. Analysis of the resultant nucleotide sequences identified a transcriptional termination signal for the expressed vlhA gene, determined the genes located downstream of the expressed vlhA gene and revealed that vlhA pseudogenes were arranged as tandem repeats upstream of the expressed vlhA gene. In order to determine whether vlhA was expressed as a monocistronic or polycistronic message, RNA from two M. synoviae clones expressing truncated or full-length versions of the vlhA gene product were purified and examined by northern blotting. Messages corresponding to the full length of the vlhA gene (approximately 2.4 kb) were detected in both clones, suggesting that truncation of the vlhA gene product was probably post-transcriptional. These studies have revealed the organization of the M. synoviae vlhA gene locus and established that the vlhA gene transcript is monocistronic.