Abstract: β-actin gene is a member of the actin family，mainly involved in maintaining cell structure，movement and physical activity in cell division, and plays an important role in quantitative genetic experiments. In this study, RT-PCR and RACE techniques were used to amplify the cDNA full-length of β-actin in the mud crab(Scylla paramamosain). Sequence analysis showed that the full cDNA of β-actin gene was 1 434 bp long, including a 1 131 bp open reading frame（ORF）, a 83 bp 5' untranslated region（5' UTR）and a 243 bp 3' untranslated region（3' UTR）. The ORF encoded 376 amino acids residues with a predicted molecular mass and PI of approximately 41.79 kD and 5.205, respectively. Multiple alignment with homologous amino acid residues was performed and it indicated a high similarity among the 18 species. Scylla paramamosain was more closely related to Gecarcinus lateralis than any other species according to the neighbor joining（NJ）phylogenetic tree. Real-time PCR results indicated that β-actin gene expressed in all eight different tissues including blood, heart, liver, stomach, gill, muscle, testis and connective tissue, with the highest expression in muscle and lowest expression in connective tissue. Owing to the significant differences of RNA expression among these tissues, this gene is not suitable used as an endogenous control.

Key words: Scylla paramamosain, β-actin gene, Gene cloning, Tissue expression, Endogenous control