The gene encoding extracellular poly(3-hydroxybutyrate) depolymerase from a thermophilic poly(3-hydroxybutyrate)-degrading bacterium, strain HS, was cloned and intracellularly expressed in Escherichia coli. The gene was found to consist of 1485-bp nucleotide sequence coding for a 22-amino-acid signal peptide and a 473-amino-acid mature protein. Phylogenetic analysis and domain structure showed that the enzyme was clustered with type II PHB depolymerases. The gene was expressed in E, coli under the control of the tac promoter. A 46-kDa protein was detected in the cell extract by SDS-PAGE. The N-terminal sequence of the protein agreed with that of the original enzyme. The crude enzyme was able to degrade PHB particles at 70 degreesC.