Sequences of the genes and polypeptide precursors for two bovine protease inhibitors.

The genes for bovine pancreatic trypsin inhibitor and a homologous protease inhibitor have been characterized using messenger RNA, clones of complementary DNA copies and genomic fragments. Both genes consist of three exons and two introns and are virtually identical in sequence, suggesting that recently they either arose by gene duplication or were subject to gene conversion. However, they differ markedly in their promoter regions and in a segment within the first intron. Perhaps as a consequence, the two genes can be expressed using different transcription start sites, and the two proteins are found in different bovine tissues. Each middle exon encodes primarily the mature protein, while the other two exons define amino- and carboxyl-terminal extensions of 33 or 35 and 7 amino acid residues, respectively. The amino-terminal extensions contain a signal peptide-like sequence, suggesting that the proteins are destined for cellular compartments. The remaining extensions at both ends may be involved in targetting of the proteins, and there are some similarities to other proteins destined for cellular compartments.