We cloned and characterized a unique and highly compartmentalized sea cucumber aromatization gene,P450c17.The full-length sea cucumber P450c17 cDNA was 2 036 bp in length,and contained a 1 530 bp open reading frame(ORF),a 250 bp 3′UTR,and a 256 bp 5′UTR.Based on the effective length of gene translation,the full-length P450c17 cDNA had ATTTA special sequences in the 3′ UTR and polyA regions.The full-length P450c17 cDNA encoded 509 amino acids constituting a 57.6 kD protein molecule with an isoelectric point of 5.5.The precursor protein was hydrophilic.The protein sequence had one signal peptide,consisting of a 25 amino acid residue.The signal peptide consisted primarily of an alpha helix.The sequence of amino acids contained one transmembrane region,involving in electronic transfer catalysis between the internal and external membrane.We found a single N-glycosylation site,suggesting the precursor protein belonged to the family of secretion trans-membrane glycoproteins.The secondary structure of the precursor protein consisted primarily of an alpha helix,with irregular coiling and a strand chain,but without β folding in the complete protein.Sequence comparison re-vealed that the similarity of the P450c17 precursor protein ranged from 35% to 41% with other aquatic animals.We conducted a phylogenetic analysis using the neighbor joining(NJ) method.The evolutionary tree indicated that the P450c17 precursor protein was clustered with the oyster and lancelet amphioxus.The P450c17 precursor pro-tein contained a P450 specific structure domain.The conserved core was composed of a coil termed the "meander",a four-helix bundle,helices J and K,and two sets of beta-sheets.These constitute the haem-binding loop(with an absolutely conserved cysteine that serves as the 5th ligand for the haem iron),the proton-transfer groove,and the absolutely conserved EXXR motif in helix K.Our results provide a reference for investigating the function of this gene.