Characterization of two members (CST4 and CST5) of the cystatin gene family and molecular evolution of cystatin genes.

Two members (CST4 and CST5) of the cystatin gene family have been characterized partially by DNA analysis. The CST4 clone contained the gene coding for the precursor form(141 amino acids) of cystatin S, and its exon-intron organization is the same as that of other members (the cystatin SN gene at the CST1 locus, the cystatin SA gene at the CST2 locus, the cystatin C gene at the CST3 locus and a cystatin pseudogene at the CSTP1 locus). The second cystatin pseudogene was elucidated in the clone, CST5, and it was assigned to the CSTP2 locus. Alignment of DNA sequences of cystatin genes with other genes suggested that the genes for cystatins, kininogens, and Bowman-Birk type inhibitors have evolved from an ancient ribonuclease-like gene.