STRUCTURAL HETEROGENEITY OF THE EMM GENE-CLUSTER IN GROUP-A STREPTOCOCCI

One or more distinct copies of emm genes lie within a gene cluster tha t is located downstream from a transcriptional regulatory gene (mry). Mry is a positive regulator for the genes in this cluster and for the downstream gene, scpA. The objective of this study is to examine the s tructure of this cluster and the distribution of specific alleles with in the cluster among group A streptococcal isolates of 32 different se rotypes. The peptidoglycan (PG)-spanning domain, which exists in four divergent forms, was used to identify specific alleles of the genes wi thin the emm cluster. Gene content of the cluster was determined by So uthern hybridization with allele-specific oligonucleotides. Five diffe rent chromosomal patterns for this cluster were observed. Sequence het erogeneity in the adjacent mry locus was demonstrated by the ability o f some of the isolates to hybridize with a whole mry gene probe, but n ot with mry-based oligonucleotide probes. A PCR-based chromosomal mapp ing technique was used to examine further the gene order within the em m gene clusters. Structural heterogeneity of the emm gene cluster was found within class I isolates in this study, while class II isolates w ere relatively homogeneous at this chromosomal locus and distinct from class I.