Using PCR, cloning and sequencing techniques, a 1.1-kb complementary DNA fragment encoding for a b-mannan- ase (mannan endo-1,4-b-mannosidase, EC 3.2.1.78) has been identified in the digestive gland of blue mussel, Mytilus edulis. The cDNA sequence shows significant sequence identity to several b-mannanases in glycoside hydrolase family 5. The b-mannanase gene has been isolated and sequenced from gill tissue of blue mussel and contains five introns. The b-mannanase has been expressed extracellularly in Pichia pastoris using the Saccharomyces cerevisiae a-factor signal sequence. The b-mannanase was produced in a 14-L fermenter with an expression level of 900 mgÆL)1. The expression level is strongly affected by the induction tem- perature. A two-step purification procedure, composed of a combination of immobilized metal ion affinity chromato-