ISOLATION AND SEQUENCE OF CDNA-ENCODING A 3-METHYLCHOLANTHRENE-INDUCIBLE CYTOCHROME-P450 FROM WILD RED-SEA BREAM, PAGRUS-MAJOR

We have isolated a cDNA clone of mRNA for the cytochrome P450 from a 3 -methylcholanthrene (MC)-treated red sea bream, Pagrus major, using a cDNA fragment for rat P4501A2 as a probe. The cloned cDNA is ca. 1.8 k b long and contains an open reading frame of 1545 nucleotides for poly peptides of 515 amino acids. The deduced N-terminal amino acid sequenc e of the cDNA is very similar to that for purified cytochrome P450 pro tein from the marine fish scup, which was reported previously (Klotz e t al. 1983). A conserved amino acid sequence containing a putative hem e-binding cysteine is present in the equivalent position proximate to the C-terminus of the molecules. The deduced amino acid sequence shows more than 50% positional identity with known members of the mammalian aromatic hydrocarbon-inducible P450 family. RNA blot analysis indicat es that P450 mRNA (s) is expressed in the liver, kidney, gill and gut of the MC-treated P. major.