CHARACTERIZATION AND DISTRIBUTION OF INSERTION-SEQUENCE IS1239 IN STREPTOCOCCUS-PYOGENES

The human pathogenic bacterium Streptococcus pyogenes causes pharyngit is, acute rheumatic fever, glomerulonephritis and toxic-shock-like syn drome. The bacterium synthesizes several extracellular products, inclu ding the recently described streptococcal superantigen SSA, a molecule that shares considerable homology with several Staphylococcus aureus enterotoxins. While studying allelic variation at the ssa locus, six i solates expressing serotypes M4, M23, M33, M41, M43, and provisional t ype PT4854, were identified that had PCR products about 40-bp larger t han expected, and one isolate (M15) had an amplified fragment that was more than 1-kb larger than expected. All six isolates have a 34-bp in sert located 103 bp 5' of the ssa start codon. The larger product is a result of a 1110-bp insertion at the analogous location. The compleme ntary strand of this insert has a 981-bp open reading frame that poten tially encodes a 326-amino-acid polypeptide with substantial homology to the Escherichia coli IS30 transposase. Results of Southern blot ana lysis showed that at least twelve copies of the sequence are present i n the serotype M15 S. pyogenes isolate. This element, designated IS123 9, is the first simple insertion sequence described in group-A strepto cocci. Results of PCR screening showed that 26 of 78 (33%) S. pyogenes isolates expressing distinct M protein serotypes contained-sequences with homology to IS1239, which means that the element is widely distri buted in the species.