Promoter sequence, exon:intron structure, and synteny of genetic location show that a chicken cytokine with T-cell proliferative activity is IL2 and not IL15

The gene encoding a chicken cytokine with T-cell proliferative activity was cloned, sequenced, and mapped. The results show that this cytokine is chicken IL2 and not IL15. The exon:intron structure of chicken IL2 corresponds almost exactly to those of mammalian IL2s with the exceptions of exon 2 and introns 2 and 3 which are shorter. Chicken IL2 contains five repeats of the "instability" motif ATTTA in the 3' untranslated region in exon 4. It is a single-copy gene, with neither structural (amino acid) nor promoter sequence polymorphisms identified. Analysis of the predicted amino acid sequence suggests that overall protein structure is conserved, but the receptor binding sites are not. A number of potential regulatory sequences similar to those found in mammals have been identified in the promoter. These include (5'-3') a composite NF-AT/"AP-1" element, a CD28 response element, an AP-1 element, an NF-AT element, and the AP-1 part of an AP-1/octamer composite element. The mammalian NF-kappa B and octamer binding sites seem to be absent, although there are alternative potential NF-kappa B and octamer-binding elements in the chicken IL2 promoter, in close proximity to their mammalian homologues. Sequence comparisons also predict other potential transcription factor binding sites as yet undescribed in mammalian IL2 promoters. A Taq I polymorphism was identified which enabled chicken IL2 to be mapped to chromosome 4, linked to ANX5, with synteny with mouse chromosome 3 and human chromosome 4. This is the first non-mammalian cytokine gene to be mapped.