Kimura S, Hanioka N, Matsunaga E, Gonzalez F J
Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD 30892.
DNA. 1989 Sep;8(7):503-16. doi: 10.1089/dna.1.1989.8.503.
The P450 CYP4A1 and CYP4A2 genes were isolated from a rat genomic library constructed in the vector lambda EMBL3 and their complete sequences were determined. The CYP4A1 and CYP4A2 genes spanned 14,144 and 10,576 bp and contained 13 and 12 exons, respectively. The CYP4A1 gene contained an additional intron that splits the exon corresponding to exon 12 of the CYP4A2 gene, resulting in a noncoding 13th exon in CYP4A1. The exon numbers of these genes were distinct among known P450 genes, and yet several intron-exon junctions along the P450 amino acid coding region were conserved with P450 genes in the CYP2, CYP11, and CYP21 gene families. On the basis of these data, the number of exons in the putative ancestral P450 gene was estimated. The evolutionary implications of this finding are discussed. No consensus TATA sequence was found upstream of either gene's transcription start site. Comparison of the CYP4A1 and CYP4A2 promoters with other genes that lack TATA boxes did not reveal any strong consensus sequence in their immediate upstream regions. However, a conserved 19-bp sequence was located at the positions of 42 and 48 bp upstream from the CYP4A1 and CYP4A2 genes' start sites, respectively. The CYP4A2 gene also contained two 378-bp direct repeats upstream from the start site; these repeats are derived from portions of the long interspersed middle repetitive element present in high copy numbers in the rat genome.
从构建于λEMBL3载体的大鼠基因组文库中分离出P450 CYP4A1和CYP4A2基因，并测定了它们的完整序列。CYP4A1和CYP4A2基因分别跨越14144和10576碱基对，分别包含13个和12个外显子。CYP4A1基因包含一个额外的内含子，该内含子将与CYP4A2基因第12外显子相对应的外显子分开，导致CYP4A1中有一个非编码的第13外显子。这些基因的外显子编号在已知的P450基因中是不同的，然而，沿P450氨基酸编码区的几个内含子-外显子连接与CYP2、CYP11和CYP21基因家族中的P450基因是保守的。基于这些数据，估计了推定的祖先P450基因中的外显子数量。讨论了这一发现的进化意义。在两个基因的转录起始位点上游均未发现共有TATA序列。将CYP4A1和CYP4A2启动子与其他缺乏TATA框的基因进行比较，在它们紧邻的上游区域未发现任何强共有序列。然而，一个保守的19碱基对序列分别位于CYP4A1和CYP4A2基因起始位点上游42和48碱基对的位置。CYP4A2基因在起始位点上游还包含两个378碱基对的直接重复序列；这些重复序列源自大鼠基因组中高拷贝数存在的长散在中间重复元件的部分。
