Molecular cloning of cDNA for SPase, a monkey cathepsin L orthologue

SPase is a cysteine protease isolated from an African green monkey kidney cell line, CV-1, and has selective cleavage activity toward transcription factor SP-1 and retinoblastoma susceptibility gene product RB. In this study, a cDNA encoding SPase was cloned from a cDNA library prepared from CV-1 cells. The cDNA clone encodes 333 amino acids and is 96.5% identical to human cathepsin L at the nucleotide and amino acid sequence levels. SPase appears to be translated as a preproenzyme based on the comparison between the deduced amino acid sequence and the N-terminal sequence of the purified enzyme. Northern blot analysis exhibited the considerably higher expression of SPase in CV-1 cells compared with COS-1 cells, showing a good correlation with enzymatic activity in these cell lines. Bacterially expressed SPase protein exhibited proteolytic activity toward SPA and RB proteins. These observations suggest that SPase is a monkey cathepsin L orthologue.