The 185/333 gene family involved in the immune response of sea urchin.One 185/333 c DNA was isolated from Strongylocentrotus intermedius,and named as Si185/333-1.Its full-length c DNA was 1246 bp in length with a 906 bp open reading frame encoding a protein of 301 aa.The molecular weight of the deduced protein was approximately 33.1 k D with an estimated PI of p H 6.26.Si185/333-1 had high identities(70%–86%) to most of Sp185/333.An extraordinary identity of 92% was found between Si185/333-1 and Sp185/333 C5 alpha(ABR22474).Moderate identities(63%–64%) were displayed between Si185/333-1 and He185/333.Si185/333-1 had similar structure to Sp185/333.A signal-peptide,a gly-rich region and a his-rich region were found in its secondary structure.RGD motif was found in gly-rich region at position 116–118aa.There was no transmembrane region in Si185/333-1.The element pattern of Si185/333-1 is different from any available pattern that identified in Sp185/333.Si185/333-1 clustered together with pattern C Sp185/333 in phylogenetic tree.The Si185/333-1 m RNA could be detected in tissues including peristomial membrane,coelomocytes,muscle of Aristotles lantern,gut and tube feet,with the highest expression level detected in peristomial membrane and a relatively low expression in ovary and testis.The temporal expression of Si185/333-1 in peristomial membrane and coelomocytes were up-regulated after bacterial,β-D-glucan and ds RNA challenges,reaching the maximum at 12 h post-stimulation.The up-regulation was more obvious in coelomocytes,and bacterial challenge triggered the highest response.These results proved that 185/333-1 gene was involved in the immune defense of S.intermedius,while more studies were necessary for its function in S.intermedius immunity. The 185/333 gene family involved in the immune response of sea urchin. One 185/333 c DNA was isolated from Strongylocentrotus intermedius, and named as Si 185 / 333-1.Its full-length c DNA was 1246 bp in length with a 906 bp open reading frame encoding a protein of 301 aa. The molecular weight of the deduced protein was approximately 33.1 k D with an estimated PI of p H 6.26.Si185 / 333-1 had high identities (70% -86%) to most of Sp185 / 333. An extraordinary identity of 92% was found between Si185 / 333-1 and Sp185 / 333 C5 alpha (ABR22474). Moderate identities (63% -64%) were displayed between Si185 / 333-1 and He185 / 333. Si185 / 333-1 had similar structure to Sp185 / 333.A signal-peptide, a gly-rich region and a his-rich region were found in its secondary structure. RGD motif was found in gly-rich region at position 116-118aa . There was no transmembrane region in Si185 / 333-1. The element pattern of Si185 / 333-1 is different from any available pattern that identifies in Sp185 / 333. Si185 / 333-1 clustered together with pattern C Sp185 / 333 in phylogenetic tree. The Si185 / 333-1 m RNA could be detected in tissues including peristomial membrane, coelomocytes, muscle of Aristotles lantern, gut and tube feet, with the highest expression level detected in peristomial membrane and a relatively low expression in ovary and testis. The temporal expression of Si185 / 333-1 in peristomial membrane and coelomocytes were up-regulated after bacterial, β-D-glucan and ds RNA challenges, reaching the maximum at 12 h post-stimulation. up-regulation was more obvious in coelomocytes, and bacterial challenge triggered the highest response. These results demonstrated that 185 / 333-1 gene was involved in the immune defense of S.intermedius, while more studies were necessary for its function in S.intermedius immunity.