IFN-ts possess approximately 75%, 50%, and 30% amino acid sequence identity with omega (w), alpha (a), and beta IFNs, respectively. The progenitor IFN-t genes (IFNT) probably arose from an ancestral IFN-cd gene (IFNW) by a duplication event that occurred approximately 36 million years ago. The IFN-ts, like other type I IFNs, are composed of five major alpha helices connected by loops, with a long loop region between helix A and В. Bovine (bo) and ovine (ov) IFN-ts have antiviral and antiproliferative activities that are comparable to those of other type I IFNs. The IFN-ts interact with the same type I IFN receptor and with affinity approximately similar to that of boIFN-a on bovine endometrium. Interestingly, however, the IFN-ts may be more potent as pregnancy hormones than other type I IFNs. BoIFN-ot also has a much poorer ability than boIFN-Tl to induce production of at least two proteins secreted from bovine endometrium. ventolin inhalers
One feature of IFN-ts, which is also present in their structural relatives, the IFN-ws, is the presence of a six amino acid extension at the carboxyl terminus, which results in polypeptides that are 172 amino acids in length rather than the standard 166 amino acids for most IFN-as. This “tail” is present on all expressed isoforms of bovine and ovine IFN-ts and may have evolved from a frame shift or a mutation in the stop codon after divergence of the IFNT/W progenitor gene from IFN-a genes (IFN A) about 130 million years ago. It has not been possible to predict the tertiary structure of this tail by using computer modeling, because such models have been based on the crystal structure of murine IFN-p, which is 163 amino acids in length. This tail may be sufficiently long (3 nm) to interact either with putative receptor binding regions on IFN-т and -w molecules themselves or with protein domains of the type I IFN receptor complex. The aim of the present study was to determine whether the signature carboxyl tail of IFN-ts contributes to their biological activities and particularly in their ability to extend CL life span in nonpregnant ewes.