ANTIGENIC DIVERSITY WITHIN A FAMILY OF M-PROTEINS FROM GROUP-A STREPTOCOCCI - EVIDENCE FOR THE ROLE OF FRAMESHIFT AND COMPENSATORY MUTATIONS

The genes (emm) encoding M proteins, from isolates of group-A streptoc occi (GAS) serotyped as M52, M53, M80 and M nontypeable (MNT; serologi cally related to M53 and M80), were examined. Characterization of emm from these GAS revealed some discrepancies with serotyping, illustrati ng the difficulty in serotype determination when cross-reactions occur . DNA sequences corresponding to the N-terminal region of M proteins f rom the isolates showed considerable similarity both in the hypervaria ble region and the repeat regions. We propose that these serotypes for m a family of closely related M types. Frameshift mutations in the hyp ervariable region followed by a corrective (compensatory) frameshift w ere observed. This may be an effective mechanism for generating antige nic diversity in the M protein.