Identification and sequencing of cDNA clones for the rodent negative acute‐phase protein α1‐inhibitor 3

Abstract

Rat α₁‐inhibitor 3 clones were isolated by immunological screening of a λ gt11 cDNA library prepared from rat liver poly(A)‐rich RNA. The recombinant cDNA clones were identified by the absence of their immunoprecipitable products following hybrid‐arrested in vitro translation. The size of the cognate poly(A)‐rich RNA was estimated to be roughly 5000 residues. Approximately 16 h after induction of inflammation the amount of α₁‐inhibitor 3 poly(A)‐rich RNA decreases as shown by dot‐blot hybridization and Northern analyses. The response of this negative acute‐phase plasma protein to inflammation may therefore be considered to be at the pretranslational level. The characterized DNA constitutes an open reading frame of 225 amino acids followed by a canonical eucaryotic polyadenylation signal and a poly(A) tail. Sequence microheterogeneity, particularly in the 3′‐flanking region was observed. An amino acid homology of 70% for α₁‐inhibitor 3 with human and rodent α₂‐macroglobulin emphasizes the evolutionary relationship of the macroglobulins.