Chicken Interferon Gene: Cloning, Expression, and Analysis

Abstract

A gene encoding chicken interferon (ChIFN) was cloned from a cDNA library made from primary chick embryo cells that had been "aged" in vitro so as to produce copious amounts of IFN upon induction. The coding region is predicted to produce a signal peptide of 31 amino acids and a mature protein of 162 amino acids with a molecular weight of 18,957. There are four potential N-glycosylation sites and six cysteine residues. Three disulfide bonds are possible, with two being common to most mammalian type I IFNs. A motif of 10 amino acids surrounding Cys-137 is highly conserved: It shows 80% homology with mammalian type I IFNs, but only 30% with a reported fish IFN. The T-rich 3′ UTR displays the canonical element AATAAA required for polyadenylation, and contains six repeats of the octamer CTATTTAT that may be involved in down-regulating translation. Northern blots demonstrate that the accumulation of ChIFN mRNA correlates with induction of ChIFN determined by bioassay. Biologically active protein was synthesized in transfected mouse L cells using mRNA prepared in vitro from the cloned sequence. This activity was neutralized by a monoclonal antibody prepared against purified ChlFN. The ChlFN gene shows sequence identity at the amino acid/nucleotide level with consensus mammalian IFNs as follows: alpha (24/23%), beta (20/24%), omega (23/43%), tau (20/43%), gamma (3/31%), and with flatfish IFN (16/35%). The conserved features of the predicted ChlFN protein and the general similarity of predicted secondary structure suggest a molecule that fits the five α-helix three-dimensional topology reported for type I mammalian IFNs. The ChlFN gene appears to have shared a common ancestry with type I mammalian IFN genes at the time of the avian and mammalian divergence about 350 million years ago, but both differ significantly from a sequence reported to code for a flatfish IFN.