MULTIGENE FAMILIES ENCODING THE MAJOR HEMAGGLUTININS IN PHYLOGENETICALLY DISTINCT MYCOPLASMAS

Mycoplasma synoviae has two major membrane antigens, MSPA and MSPB, bo th of which are phase variable and which may be coordinately involved in adhesion of the organism to erythrocytes. A single gene (vlhA) from M synoviae was characterized, and polypeptides were expressed from no noverlapping 5' and 3' regions in Escherichia coli. The expression pro duct of the vlhA 5' region reacted with specific reagents against MSPB , while that of the 3' region reacted with specific reagents against M SPA. Analysis of the predicted amino acid sequence showed a characteri stic signal peptidase II cleavage site, and the presence of the acylat ion site was confirmed by identification of a lipid-associated membran e protein, similar in molecular mass to MSPB, in [H-3] palmitate-label led membrane proteins. Further sequence analysis of the vlhA gene reve aled a high identity with the Il Mycoplasma gallisepticum pMGA1.7 gene , a member of a large translated family. The vlhA gene was shown to hy bridize to multiple restriction fragments of the,II. synoviae genome, suggesting that it was also a member of a multigene family. These find ings indicate that coordinate phase variation of the hco major surface antigens of M. synoviae WVU may be due to their expression from the s ame gene and that homologous gene families encode the major hemaggluti nins of two phylogenetically distinct mycoplasmas. The presence of hom ologous multigene families in such phylogenetically distinct species, but not in the genomes of more closely related species, suggests that the families may have been transferred horizontally.