Cloning of cDNA for the bovine IL-2 receptor (bovine Tac antigen)

We have cloned the Tac analog of the bovine IL-2 receptor (IL-2R) cDNA. Using mouse and human cDNA probes, we isolated five bovine IL-2R clones from a lambda gt11 bovine long-term lymphocyte cDNA library. Three of the clones had inserts of 2600 base pairs (bp), the same size as the bovine IL-2R mRNA visualized on Northern blots. The full-length cDNA contain a 190-bp 5' untranslated region, followed by a 825-bp coding region, and a 3' untranslated region that contain 1600 bp. Comparison of the bovine and human IL-2R-coding sequences revealed 71% homology at the nucleotide level. The 3' and 5' non-coding regions were not as homologous, apart from a specific site in the 5'-untranslated region that contained a 5'-upstream start codon. In this region, 24 of 26 nucleotides were identical for the human and bovine cDNAs. Further analysis of the bovine IL-2R sequence also revealed the following: (i) the hydrophobic domains of the IL-2R protein were more conserved between species than the hydrophilic domains, (ii) the predominant site of intracellular IL-2R phosphorylation in mouse and human was a conserved Ser which was not conserved in the bovine sequence, and (iii) there exists a statistically significant amino acid homology with the AIDS gag protein.