Abstract：Ribosomal protein has been proved to play an important role in protein synthesis, cell proliferation, apoptosis, development and some kinds of regulation. In order to investigate the physiological role of ribosomal protein gene in sea cucumber, full-length cDNA sequence of ribosomal protein L17(RPL17) gene was cloned from the body wall of sea cucumber (Apostichopus japonicus) using molecular cloning method in this study. The results showed that the cDNA (GenBank accession No. JQ922561) length was 643 bp, including the 33 bp of the 5'-UTR and 58 bp of the 3'-UTR. The open reading frame was 522 bp, which encoding polypeptides of 183 amino acids, with a calculated relative molecular mass of 21.5010 kD and pI of 10.29. The RPL17 was a kind of hydrophilic and unstable protein, with grand average of hydropathicity (GRAVY) of －0.964. By Blastn and Blastx searching in NCBI, the sea cucumber homologies of gene sequence and deduced amino acid sequence of RPL17 with other kinds of animals were over 70%, and the homologies between the sea cucumber and sea urchin (Strongylocentrotus purpuratus) were 75% and 81%, respectively. The predicted secondary structure of RPL17 was consisted of four recondary structure elements, including 36.61% of alpha helix, 7.65% of beta turn, 42.08% of random coil and 13.66% of extended strand. The RPL17 contained 1 functional site (RPL22 signature site)and 9 phosphorylated sites (3 cAMP- and cGMP-dependent protein kinase phosphorylation sites, 4 Protein kinase C phosphorylation sites and 2 casein kinase II phosphorylation sites). Phylogenetic relationship analysis, which was similar to the results of the biological classification, indicated that A. japonicus was firstly clustered with S. purpuratus, and also closely related with Ciona intestinalis and Xenopus laevis. And all vertebrates were clustered together. Real-time PCR was performed to analyze the expression profiling of RPL17, results showed that mRNA of RPL17 could be expressed in 5 different tissues in sea cucumber. The highest expression levels occurred in coelomocytes(P<0.01), and then in the intestine(P<0.05), body wall and longitudinal muscle. There were no significant differences in the following two tissues. The lowest expression was detected in the respiratory tree. The relative expression level in coelomocytes was 5.67, 21.63, 43.25 and 346 folds of those in intestine, body wall, longitudinal muscle and the respiratory tree. The sequences and mRNA expression level of RPL17 can be a necessary basis of study in mechanism of protein synthesis, regenerate and other physiological regulation in sea cucumber.
