MOLECULAR-CLONING AND PRIMARY STRUCTURE OF RAT ALPHA-1-ANTITRYPSIN

A cDNA clone encoding rat α1-antitrypsin has been isolated from a λgt-11 rat liver cDNA library using an antigen-overlay immunoscreening method. The nucleotide sequence of this cDNA clone is 1306 base pairs in length and has a coding region of 1224 base pairs which can be translated into an α1,-antitrypsin precursor protein consisting of 408 amino acid residues. The cDNA sequence contains a termination codon, TAA, at position 1162 and a polyadenylation signal sequence, AATAAT, at position 1212. The calculated molecular weight of the translated mature protein is 43 700 with 387 amino acid residues; this differs from purified rat (α1-antitrypsin's apparent molecular weight of 54000 because of glycosylation. Five potential glycosylation sites were identified on the basis of the cDNA sequence. The translated mature protein sequence from the cDNA clone matches completely with the N-terminal 33 amino acids of purified rat α1-antitrypsin, which has an N-terminal Glu. The cDNA encoding rat α1-antitrypsin shares 70% and 80% sequence identity with its human and mouse counterparts, respectively. The reactive center sequence of rat α1antitrypsin is highly conserved with respect to human α1-antitrypsin, both having Met-Ser at the Pl and Pl′ residues. Genomic Southern blot analysis yielded a simple banding pattern, suggesting that the rat α1-antitrypsin gene is single-copy. Northern blot analysis using the cDNA probe showed that rat α1-antitrypsin is expressed at high levels in the liver and at low levels in the submandibular gland and the lung. Dot blot analysis showed that rat α1-antitrypsin RNA levels in the liver increased by 2-fold after induction by acute-phase inflammation and that it is sexually dimorphoric, with 5-fold higher levels in male than in female rats. © 1990, American Chemical Society. All rights reserved.