Molecular basis of the variable expression of adhesins in pathogenic mycoplasmas

Variable expression of Mycoplasma gallisepticum and M. synoviae immunodominant adhesins plays the major role in the infections of poultry and is important for their diagnosis and vaccine preparations. In M. synoviae its hemadherence-positive phenotype disappearance is closely associated with truncated hemagglutinin forms and only the 27-30 kDa N-terminal part is synthesized. Thus, the C-terminal part of the hemagglutinin which enables M. synoviae attachment onto cells is lost. Switches from the hemadherence-positive to negative phenotype or inverse occur in a few % of the population. We hypothesize that they occur due to localized reversible mutations in the 5''-end of vlhA gene. Such mutations presumably introduce the termination codon TAG what results with an early termination of the protein translation and with the appearance of truncated hemagglutinin forms. Similar mutations seem to occur in pMGA1.7 gene of M. gallisepticum. Using molecular analyses we shall try to prove such reversible mutations in vlhA genes and pMGA1.7 gene and their influence on hemagglutinins synthesis. The genetic bases of the antigenic diversity of M. synoviae hemagglutinins will be determined, as well as the number of vlhA genes, their transcription and their relatedness with the pMGA genes family.