Abstract: Cytochrome P450 monooxygenases(P450s) are a superfamily of genes encoding multifunctional heme-thiolate proteins that play a dominant role in the metabolism of a wide variety of both endogenous and xenobiotic substances. The total number of P450 genes in insects registered in the GenBank is over 1 000. Most of the registered P450 gene sequences are from Diptera (74%) and Lepidoptera (16%). Of the total full-length sequences of P450 genes of insects registered, 20% are CYP6 members and 45% CYP4 members. A novel phylogenetic tree of the insect P450 superfamily which expounds evolutionary relationship of different subfamilies and orders was here constructed using a multiple alignment of the registered insect P450 sequences. The relationships of insect orders revealed by the phylogenetic tree most match the evolutionary relationships of insect orders based on other molecular data or morphological taxonomy. The present research indicates that the expression of cytochrome P450 genes may be regulated by cis-acting element or/and trans-acting factor, and the regulation mechanisms may involve the transcription enhancement (transcriptional mechanism) or an increase in mRNA stability (post-transcriptional mechanism).

Key words: Cytochrome P450, diversity, evolutionary relationship, gene expression and regulation