LACK OF POLYMORPHISM WITHIN THE RIBOSOMAL-RNA OPERONS OF GROUP-A STREPTOCOCCI

Polymerase chain reaction (PCR) ribotyping of many bacterial species h as shown that polymorphism of the ribosomal RNA (rRNA) operons, within and between strains, is common. Restriction fragment length polymorph ism (RFLP) analysis of the rRNA operons of thirty-two genetically and geographically distinct strains of group A streptococci (GAS) revealed that there are only two major HaeIII PCR-ribotypes. This variation is due to a single nucleotide change within the 16S-23S intergenic space r regions of these operons. As in many other bacterial species, this s pacer region in streptococci also contains the gene for tRNA(ala). Wit hin each GAS isolate, hybridization results are consistent with the pr esence of six rRNA operons. Interestingly, for a given strain, irrespe ctive of its origin, all six rRNA operons have the same RFLP pattern. This contrasts with the findings in many other bacterial species, wher e heterogeneity of the rRNA operons within a genome is a common featur e. This lack of heterogeneity of rRNA operons in an organism that is k nown to acquire genetic sequences through horizontal transfer is intri guing.