CLONING OF THE CDNA-ENCODING HUMAN BRAIN TRYPSINOGEN AND CHARACTERIZATION OF ITS PRODUCT

We designed degenerated oligodeoxyribonucleotide primers derived from amino acid (aa) sequences of the highly conserved active sites of mamm alian serine proteases (SPs). These primers were used to selectively a mplify, in polymerase chain reactions (PCRs), cDNA fragments coding fo r a SP. We used poly(A)(+)RNA from human brain to obtain cDNA fragment s and amplified one cDNA encoding a novel SP. The full-length nucleoti de (nt) sequence was identified by PCR and screening a genomic library in order to obtain the 5'-region. The deduced aa sequence shows a hig h degree of homology to trypsinogens, except for the first exon. In ad dition to this brain-specific trypsinogen, there exists a variant of t he cDNA in pancreas, differing only in the nt sequence of the first ex on. An active form of the trypsin was synthesized in vitro and purifie d by affinity chromatography using soybean trypsin inhibitor (STI) aga rose to demonstrate the trypsin-specific interaction with a naturally occurring inhibitor of trypsins.