Isolation of a human cDNA for alpha 2-thiol proteinase inhibitor and its identity with low molecular weight kininogen.

A lambda gt11 cDNA library containing DNA inserts prepared from human liver mRNA has been screened with an antibody to human alpha 2-thiol proteinase inhibitor that was isolated from fresh plasma. Eighteen positive clones were isolated from one million phage, and each was plaque purified. The cDNA insert of one of these phage was sequenced and shown to code for alpha 2-thiol proteinase inhibitor as identified by a partial amino acid sequence of the light chain of alpha 2-thiol proteinase inhibitor. This cDNA insert contained 1529 base pairs coding for the complete alpha 2-thiol proteinase inhibitor. It included 45 base pairs of 5' noncoding sequence, 1281 base pairs that code for pre alpha 2-thiol proteinase inhibitor, a stop codon, 160 base pairs of 3' noncoding sequence, and 40 base pairs of poly(A) tail. The noncoding sequence on the 3' end contained a potential recognition site (AATAAA) for processing and polyadenylation of precursor messenger RNA. The amino acid sequence of alpha 2-thiol proteinase inhibitor deduced from the cDNA showed a striking similarity (overall homology at 74%) to that of bovine low molecular weight (LMW) kininogen, including two internally repeated sequences and a nonapeptide sequence of bradykinin. These data clearly indicated that alpha 2-thiol proteinase inhibitor and LMW kininogen are identical. This was further supported by immunological cross-reactivity between alpha 2-thiol proteinase inhibitor and LMW kininogen.(ABSTRACT TRUNCATED AT 250 WORDS)