Streptococcus cricetus antigen I/II (paaA) 遺伝子周辺配列の解析

Antigen I/II protein is a cell surface protein antigen of Streptococcus mutans and is implicated in the adhesion mechanism to tooth surfaces. We have identified the antigen I/II homologous gene (paaA) from Streptococcus cricetus, a member of mutans streptococci. To clarify the mechanism of paaA expression, we sequenced the flanking regions of the paaA gene utilizing the gene-walking method in this study. In the upstream region of paaA, three homologous genes found in the corresponding region of Streptococcus sobrinus were identified. One of the corresponding genes in S. sobrinus was par, which has been characterized as a transcription represser of the antigen I/II (spaA) gene. Therefore, the homologous gene in S. cricetus could have a role in transcription of paaA. In the downstream region of paaA, the paaA homologous gene was found and designated as paaB. The paaB gene was interrupted by a novel insertion sequence element (ISScr1), a member of the IS982 family. Southern hybridization analysis of S. cricetus par indicated that no gene homologous to S. cricetus par was found in the oral streptococci used in this study. Furthermore, the downstream region of antigen I/II (spaA) in S. sobrinus was sequenced using the gene-walking method. No similar gene to antigen I/II gene was found in the region. It was suggested that the paaA might be regulated by the par in S. cricetus.