A single exon codes for the enzyme domain of a protozoan cysteine protease

Abstract

Theileria parva is an intracellular protozoan parasite of cattle. We have determined the nucleotide sequence of a gene and cDNA coding for a cysteine protease of T. parva. The gene is divided into two exons. The first exon codes for a signal sequence and for part of the "pro" region of the zymogen. The second exon codes for the remainder of the pro region, including residues thought to be involved in zymogen processing, and for the entire enzyme domain. Part of this exon cross-hybridizes, at high stringency, with DNA isolated from Plasmodium falciparum. It is likely that the T. parva gene is functionally active. Parasite extracts contain hydrolytic activity against benzyloxycarbonyl-Phe-Arg-7-amido-4-methylcoumarin. This activity is optimal at pH 6.0 and is inhibited by the cysteine protease inhibitor L-trans-epoxysuccinyl-leucylamido(4-guanidino)butane (E-64). This is, to our knowledge, the first description of a gene coding for a eukaryotic cysteine protease which lacks an intron in DNA coding for the enzyme domain.