Cystatin, a superfamily of cysteine proteinase inhibitors related to cathepsins and other cysteine proteinases, is widely distributed in animal tissues and body fluids. Although considerable attention has been given to mammalian and avian cystatins, little data exist on cystatins from other vertebrates. In order to isolate fish cystatin cDNA, total RNAs were isolated from liver tissues of the Chinese sturgeon (Acipenser sinensis) and Amur sturgeon (Acipenser schrenckii), respectively. The cDNAs encoding the mature peptides of cystatin and the 3′ untranslated region of the two species of sturgeon were amplified by reverse transcription polymerase chain reaction (RT PCR) using total RNA as a template. The amplified cDNA fragments were inserted into pGEM T Easy vector and sequenced and the amino acid sequences deduced. Nucleotide sequence analysis showed that both cDNAs encode 112 amino acid residues of the mature cystatin peptide. The similarity of the two sturgeon nucleotide sequence coding regions and the deduced amino acid sequences were 99 4% and 100%, respectively. Analysis of the amino acid sequences indicate that the cloned cystatins were the homolog of the mammalian cystatin C. The amino acid residues of the functional regions are well conserved among different species, but there is considerable divergence in large portions of the coding region of two sturgeon cystatins in a variety of species.
