The polyhydroxyalkanoic acid synthase gene from Chromobacterium violaceum (phaC_Cv) was cloned and characterized. A 6.3-kb BamHI fragment was found to contain both phaC_Cv and the polyhydroxyalkanoic acid (PHA)-specific 3-ketothiolase (phaA_Cv). Escherichia coli strains harboring this fragment produced significant levels of PHA synthase and 3-ketothiolase, as judged by their activities. While C. violaceum accumulated poly(3-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate) when grown on a fatty acid carbon source, Klebsiella aerogenes and Ralstonia eutropha (formerly Alcaligenes eutrophus), harboring phaC_Cv, accumulated the above-mentioned polymers and, additionally, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) when even-chain-length fatty acids were utilized as the carbon source. This finding suggests that the metabolic environments of these organisms are sufficiently different to alter the product range of the C. violaceum PHA synthase. Neither recombinant E. coli nor recombinant Pseudomonas putida harboring phaC_Cv accumulated significant levels of PHA. Sequence analysis of the phaC_Cv product shows homology with several PHA synthases, most notably a 48% identity with that of Alcaligenes latus (GenBank accession no. AAD10274).