A dextranase-encoding cDNA from L. starkeyi KSM22 was isolated and characterized.The 2052 bp cDNA fragment (lsd1 ) harbouring the dextranase gene exhibited oneopen reading frame (ORF) composed of 1824 bp flanked by a 41 bp 5′-UTR and a184 bp 3′-UTR, including a 27 bp poly(A) tail. The lsd1 gene contains no introns. Theopen reading frame encodes a 608 amino acid polypeptide (LSD1) with a 67.6 kDapredicted molecular mass. There was a 77% deduced amino acid sequence identitybetween the LSD1 dextranase and the dextranase from Penicillium minioluteum. Theprimary structure of LSD1 dextranase exhibits distant similarity with the enzymes ofthe glycosyl hydrolase family 49 that comprises Penicillium dextranase. The optimumpH of LSD1 was 6.0 and the optimum temperature was 37 ◦C. LSD1 dextranaseactivity was substantially abolished by exposure to 1 m M Hg 2+, Ag 3+ and Mn2+.LSD1 exhibited high hydrolysing activity towards dextran (100%), soluble starch(22%) and mutan (8%). Copyright 2005 John Wiley & Sons, Ltd.