Purification and characterization of the expression product of the sr gene of Streptococcus mutans OMZ 175.

The subcloning in pBR322 of the gene of the S. mutans OMZ 175 74K SR protein, was performed after in vitro reconstitution, from two recombinant EMBL3 phages, lambda SmAD9 and lambda SmAD10. The gene is expressed in E. coli HB101 under the control of its own promoter and produces a protein with a molecular weight of 195 kDa. A strong immunological relationship between the expressed protein and the 74K SR protein was observed in ELISA, Western blotting and immunoprecipitation. The 195 kDa protein was purified by immunoaffinity chromatography to homogeneity as judged by SDS-PAGE and native PAGE. Its reactivity with monoclonal anti 74K SR antibodies indicates that it is probably a precursor form of the 74K SR protein produced in S. mutans. The adhesion properties of the two proteins, tested in solid phase adherence assays, are quite similar. This indicates that the additional peptide present in the precursor protein has little or no role in the adherence properties of protein 74K SR.