MOLECULAR POPULATION GENETIC-ANALYSIS OF THE STREPTOKINASE GENE OF STREPTOCOCCUS-PYOGENES - MOSAIC ALLELES GENERATED BY RECOMBINATION

To understand the mechanisms governing molecular evolution of the stre ptokinase gene (skn), a 384bp DNA fragment encoding two variable regio ns of the molecule was characterized in 47 isolates of Streptococcus p yogenes. The results reveal that alleles of the streptokinase gene sla ve a mosaic structure, and provide strong evidence for intragenic reco mbination. Moreover, organisms that are well differentiated in overall chromosomal character have identical skn alleles, which suggests that horizontal gene transfer and recombination have participated in the e volution of this locus. No simple relationship between slap allele and serum opacity factor production or specific disease was identified. T he predicted amino acid sequences of highly divergent skn alleles are strikingly similar in hydrophilicity and hydrophobicity profiles, dist ribution of amphipathic and flexible regions, surface probability plot s, and antigenic indices, indicating that despite extensive nucleotide polymorphism in the two skn variable regions, selective pressure has constrained overall structural divergence, These results add to an imp ortant emerging theme that intragenic recombination plays a critical r ole in diversifying genes coding for streptococcal virulence factors.