A cytochrome P4501B gene from a fish species

The cytochrome P4501A (CYP1A) gene products of vertebrates are the major catalysts of polyaromatic hydrocarbon (PAH) hydroxylation and are therefore critical determinants of the pathways leading to pollutant detoxification and excretion on the one hand, or DNA-adduct formation and carcinogenesis on the other. In addition, the levels of CYP1A transcripts and protein rise in response to PAH and polyhalogenated hydrocarbons and this phenomenon has led to the development of widely used biomonitoring tools to determine pollutant exposure in wild fish populations. Recently a second CYP1 family (CYP1B) of genes has been isolated from mammals and, in common with CYP1A genes, they are transcriptionally activated by PAH and their protein products metabolise PAH. Phylogenetic analyses of CYP1 family sequences show that the CYP1A and CYP1B genes diverged long before the evolutionary emergence of mammals, suggesting that CYP1B genes may exist in fish species. If this is true then there may be important implications, both for fish health and for biomonitoring programs. In order to test this hypothesis, a plaice (Pleuronectes platessa) genomic DNA library was screened at low stringency with a plaice CYP1A6 cDNA. Amongst the resulting hybridising clones, a plaice CYP1B-related sequence was isolated. The structure, sequence and tissue expression profile of this sequence conclusively show it to be a plaice CYP1B gene.