Cloning, Expression And Characterization Of Translationally Controlled Tumor Protein (TCTP) Gene From Flatfish Turbot Scophthalmus Maximus

The translationally controlled tumor protein (TCTP) has attracted the attention of many researchers for its important role in various biological and cellular processes, such as cell growth, cell cycle progression and tumor reversion. It is ubiquitously expressed in many eukaryotic organisms, but has not been reported in turbot Scophthalmus maximus to date. In this study, a full-length cDNA encoding TCTP has been firstly isolated from the marine flatfish turbot by rapid amplification of cDNA Ends (RACE), named SmTCTP. The SmTCTP consists of a complete 5'untranslated region (UTR) of 84 bp, a 3'UTR of 451 bp and an open reading frame (ORF) of 513 bp. The ORF encodes a predicted protein of 170 amino acid residues named SmTCTP, containing two signature sequences of TCTP family, TCTP1 and TCTP2. It has several potential phosphorylation sites. The 5'UTR of SmTCTP starts with a 5'-terminal oligopyrimidine tract (5'-TOP), a typical feature for translationally controlled mRNAs. The deduced amino acid sequence of SmTCTP displays higher and similar homology to the other known vertebrate TCTPs (58.8%~64.1%) than invertebrates. However, the length of fish TCTP was different among species with 170 amino acids in turbot and sea perch, while 171 amino acids in zebrafish and rohu. The phylogenetic tree reveals that the turbot is clustered together with three fishes, as well as Xenopus laevis. Northern blot analysis of SmTCTP from the normal, albino and ventral skins reveals that its expression level in albino skin is slightly higher than normal skin. Also, it indicates that there is only one mRNA transcript for SmTCTP, which is similar to rohu but different from mammals human and rabbit. The pET30a-SmTCTP expression plasmid has been successfully constructed, and the fusion protein has been over-expressed in E.coli. The target fusion protein of His-tag SmTCTP has been further purified and identified by peptide mass fingerprinting. This study is the first report about TCTP in Turbot. It paves the way for further investigation of the biological functions of TCTP in fish.