The complete nucleotide sequence of the Streptococcus mutans GS-5 scrB gene coding for sucrose-6-phosphate hydrolase activity was determined. A potential ribosome-binding site as well as promoter sequences were identified upstream from the gene. The deduced amino acid sequence of the enzyme suggested a molecular weight of 51,750, which is similar to that estimated for the enzyme isolated from strain GS-5. The enzyme is slightly acidic, with a pI of 5.9, and is a relatively hydrophilic protein. The nucleotide and amino acid sequences of the enzyme showed significant homology with those of the sacA protein from Bacillus subtilis. In addition, a region of amino acid homology with the S. mutans fructosyltransferase and B. subtilis levansucrase proteins was also detected.
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