Elucidation of a unique regulatory mechanism for scrA gene expression in S.mutans

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We have investigated regulatory mechanisms of the scrA gene encoding EnzymeII of sucrose PTS from S.mutans. Expression of the scrA gene was regulated not only by sucrose but also by sorbitol. In order to elucidate molecular mechanisms of this characteristic regulation, we launched two projects :1) Characterization of putative ORFs franking the scrA and scrB genes. 2) Cloning of sorbitol transport genes.ORFs downstream from the scrA gene were identified as the scrK and pmi genes encoding fructokinase and phosphomannose isomerase respectively. Northern analysis revealed that these genes consisting an operon were transcribed independently of the scrA gene. Another ORF (ds2ORF3) downstream from the scrB gene did not involve in scrA or scrB regulation but interestingly involved stress-induced glucan-dependent aggregation. Although the mechanism of the aggregation in detail remains to be resolved, we could have established a method to clone genes directly involved in the aggregation.During a process to clone sorbitol transport genes, two other genes have been cloned. One was identified as the pfl gene encoding pyruvate formate-lyase that is the key enzyme of sugar metabolism of streptococci. The other was similar to the putative positive regulator gene of S.gordonii glucosyltransferase. Since these genes should be important for cariogenisity of S.mutans, they have to be characterized in future together with ds2ORF3.We could identify all genes essential for sucrose metabolism of S.mutans. Although we could not elucidate mechanisms of the unique scrA expression within this period, study has expanded to unexpected derections.