ISOLATION OF CYP3A5P CDNA FROM HUMAN LIVER - A REFLECTION OF A NOVEL CYTOCHROME-P-450 PSEUDOGENE

We have isolated, from a human liver cDNA library, a 1627 bp CYP3A5 cD NA variant (CYP3A5P) that contains several large insertions, deletions , and in-frame termination codons. By comparison with the genomic stru cture of other CYP3A genes, the major insertions in CYP3A5P cDNA demar cate the inferred sites of several CYP3A5 exons. The segments inserted in CYP3A5P have no homology with splice donor acceptor sites. It is u nlikely that CYP3A5P cDNA represents an artifact of the cloning proced ures since Southern blot analysis of human genomic DNA disclosed that CYP3A5P cDNA hybridized with a DNA fragment distinct from fragments th at hybridized with either CYP3A5, CYP3A3 or CYP3A4. Moreover, analysis of adult human liver RNA on Northern blots hybridized with a CYP3A5P cDNA fragment revealed the presence of an mRNA with the predicted size of CYP3A5P. We conclude that CYP3A5P cDNA was derived from a separate gene, CYP3A5P, most likely a pseudogene evolved from CYP3A5.