Cloning and Phylogenetic
Analysis of Interleukin-2 Gene in Xiaoshan Chicken, A Chinese Local Chicken
Breed
LI Jian-Rong, HUANG Yao-Wei, MENG Song-Shu, LIANG Xue-Ya,
XIE Rong-Hui, YU Lian*
( Institute of Preventive Veterinary Medicine, Zhejiang University,
Hangzhou 310039, China )
Abstract Chicken
interleukin 2 (cIL-2) is one of important nonmammalian cytokines isolated
recently. In this paper, optimum condition for production of chicken IL-2 in
vitro was developed. Isolation of spleen lymphocytes from Xiaoshan
chicken, activation by ConA, followed by RT-PCR in a single step, resulted in
the synthesis of chicken IL-2 cDNA. The full-length chicken IL-2
cDNA was 737 bp, encoding a 143 amino acids precursor. Only 1–5 amino acid
difference were found compared with other three published chicken IL-2s. This
IL-2 shared 69.4% homology with turkey IL-2 and shared 21.2%–9.4% homology
with mammalian IL-2. The predicted protein had a leader sequence composed of 22
amino acids, and four conversed cysteines allowing the formation of two
intrachain disulfide bonds. There were four regions of heptad repeats, with
hydrophobic amino acids at positions 1 and 4, were presumably forming
amphipathic α-helices. These regions were equivalent to mammalian helices A, B,
C and D. The amino acids at positions 40(D), 65(Y), 82(E), 108(N) and 142(Q)
might play roles in binding to receptors of chicken IL-2. Phylogenetic tree
analysis indicated that the chicken IL-2 may have evolutionary relationship
with mammalian IL-2； they showed however species difference
in function because of selective pressure of immune systems.
Key words chicken interleukin 2 (cIL-2)； cloning； sequence analysis； phylogenetic analysis
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