Identification of a New Human CYP2A Gene Fragment with Close Linkage to CYP2GP1

Human genomic libraries were screened to identify CYP2G -related cytochrome P450 genes. A genomic fragment comprising exons 7 through 9 of CYP2GP1 and exons 6 through 9 of a previously unidentified CYP2A gene, designated CYP2A7P2 , was isolated from an EMBL3 library; the two genes were arranged in outward opposite directions with about 8 kbp of intervening sequence. The same structure was also detected in a bacteriophage P1 clone, which contained a full-length CYP2GP1 gene, exons 6 through 9 of CYP2A7P2 , and the CYP2B7 gene. However, additional CYP2A -related exons as well as other CYP2A genes, CYP2A7P1 , CYP2B6 , CYP2F1 , and CYP2GP2 were not detected. These results indicate that CYP2A7P2 is located near CYP2B7 in the middle of the CYP2A-2B-2F gene cluster on chromosome 19. Furthermore, an analysis of CYP2A sequence alignment suggests that CYP2A7P2 may be derived from the same ancestral gene that gave rise to CYP2A7P1 , which was corrupted by a large insertion at intron 5.