The human cathepsin F gene--a fusion product between an ancestral cathepsin and cystatin gene.

Human cathepsin F is a novel papain-like cysteine protease of unknown function. Here, we describe the complete human cathepsin F (CTSF) gene which is composed of 13 exons. In addition to a previous report, two novel upstream located exons whose splice sites interrupted the propeptide of cathepsin F within the 'cystatin-like' domain, recently described by Nagler et al. (Biochem. Biophys. Res. Comm. 257, 313-318, 1999) were identified. A comparison of the genomic structures between this novel part of the cathepsin F gene and those of several cystatin genes revealed striking similarities, supporting the hypothesis that the cathepsin F gene resulted from a gene fusion between an ancestral cystatin and cathepsin gene.