A cDNA encoding thyroid stimulating hormone beta-subunit (TSHbeta) was cloned from pituitary of the Chinese soft-shell turtle, Pelodiscus sinensis, and its regulation of mRNA expression was investigated for the first time in reptile. The Chinese soft-shell turtle TSHbeta cDNA was cloned from pituitary RNA by reverse transcription and polymerase chain reaction (RT-PCR), and rapid amplification cDNA end (RACE) methods. The Chinese soft-shell turtle TSHbeta cDNA consists of 580-bp nucleotides, including 67-bp nucleotides of 5'-untranslated region (UTR), 402-bp of the open reading frame, and 97-bp of 3'-UTR followed by a 14 poly (A) trait. It encodes a precursor protein molecule of 133 amino acids with a putative signal peptide of 19 amino acids and a putative mature protein of 114 amino acids. The number and position of 12 cysteine residues, presumably forming six disulfide bonds, one putative asparagine-linked glycosylation site, and six proline residues that are found at positions for changing the backbone direction of the protein have been conserved in the turtle as in other vertebrate groups. The deduced amino acid sequence of the Chinese soft-shell turtle TSHbeta mature protein shares identities of 82-83% with birds, 71-72% with mammals, 49-57% with amphibians, and 44-61% with fish. The Chinese soft-shell turtle pituitaries were incubated in vitro with synthetic TRH (TSH-releasing hormone), thyroxine and triiodothyronine at doses of 10(-10) and 10(-8)M. TRH stimulated, while thyroid hormones suppressed, TSHbeta mRNA levels in dose-related manner. The sequences of cDNA and its deduced peptide of TSHbeta as well as the regulation of its mRNA level were reported for the first time in reptile.