The chiA gene encoding chitinase A was cloned into Escherichia coli from Xanthomonas sp. strain AK and its nucleotide sequence was determined. The structural gene consists of 1788 bp encoding 596 amino acids with a predicted molecular weight of 62,122. The deduced ChiA is a modular enzyme composed of an N-terminal signal peptide and four domains in the following order: a chitin-binding domain, two fibronectin type III domains, and a family 18 catalytic domain. ChiA purified from the recombinant E. coli had temperature and pH optima at 35 degrees C and 4.5, respectively. The K-m and V-max values for colloidal chitin were estimated to be 1.8 mg/ml and 8.7 mu mol/min/mg, respectively.