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

Antigenic variants of Mycoplasma gallisepticum major surface lipoprotein. p MGA, are encoded by a large gene family. In this study sequence analyses of the PCR-amplified pMGA genes showed two types of sequences similar to the pMGA1.2 gene in M. gallisepticum strains. They differed in the sequence enc oding a proline-rich region (PRR) at the N-terminus of the pMGA protein. Th e type A genes had sequences similar to the published pMGA1.2 gene sequence of strain S6, whereas the type B genes lacked the second repetitive segmen t encoding PTPN sequence within PRR and were similar to the published seque nce of PG31 strain. Low in vitro passages of M. gallisepticum strains isola ted recently in Slovenia from four avian species showed very different expr ession patterns of pMGA1.2 and pMGA1.9 genes. Among isogenic populations of S6(B) and IHB1 strains a high frequency of pMGA antigenic variants lacking an epitope for monoclonal antibody (mAb) 71 was found. Strain IHB1 clones, which synthesized pMGA recognized by mAb 71, transcribed pMGA genes whose partial sequence encoded the amino acid sequence (262)TNGDEPRSVS of the mAb 71 epitope. Other IHB1 clones synthesized pMGA variants with different iso electric points, lacking the epitope for mAb 71, but expressing downstream epitopes for other mAbs. Our study suggests that a molecular basis for pMGA antigenic variation lies in the corresponding changes at the DNA level. (C ) 2000 Federation of European Microbiological Societies. Published by Elsev ier Science B.V. All rights reserved.