Localization and sequence analysis of the phnH gene encoding 2-hydroxypent-2,4-dienoate hydratase in Pseudomonas sp. strain DJ77.

The phnDEFG genes of Pseudomonas sp. DJ77, which are responsible for the degradation of polyaromatic hydrocarbons and chlorinated aromatics, were located previously on the 6.8 kb XhoI fragment of chromosomal DNA. Here, we sequenced a downstream region hitherto unknown and identified the phnH gene encoding a 2-hydroxypent-2,4-dienoate hydratase, which is required for the conversion of 2-hydroxypent-2,4-dienoate to 4-hydroxy-2-oxovalerate in the meta-cleavage pathway of catechols. The relative position of the hydratase gene in the phn operon is unique compared to the other meta-cleavage operons which have a dehydrogenative branch of the pathway. The PhnH hydratase contains 264 amino acids with a Mr of 28048. The deduced amino acid sequence of the PhnH enzyme is 60.9-31.6% identical to those of homologous enzymes encoded by the todG, bphE, cmtF, bphH, bphX1, xylJ, dmpE, cumE, MTCY03C7.20 and etbE genes.