CLONING AND SEQUENCING OF THE GENE CODING FOR DEXTRANASE FROM STREPTOCOCCUS-SALIVARIUS

We cloned and sequenced the dextranase (Dex) (1,6-alpha-glucanhydrolas e; EC 3.2.1.11)-encoding gene from Streptococcus salivarius (Ss) strai n M-33. Recombinant clones from an Ss genomic library specifying Dex a ctivity were identified as colonies surrounded by transparent halos on blue dextran plates. One of the clones had a 4.3-kb KpnI fragment con taining the gene coding for an 826-amino-acid polypeptide with a molec ular mass of 87.9 kDa, which corresponds well to that of native Dex fr om the Ss culture supernatant. There was no sequence homology between the gene encoding Ss Dex and the gene encoding dextran glucosidase of S. mutans, or between their protein products.