Cloning and Phylogenetic Analysis of Interleukin-2 Gene in Xiaoshan Chicken, A Chinese Local Chicken Breed.
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 alpha-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.
Li
J R
JR
Institute of Preventive Veterinary Medicine, Zhejiang University, Hangzhou 310039, China. yulian@zju.edu.cn
Huang
Y W
YW
Meng
S S
SS
Liang
X Y
XY
Xie
R H
RH
Yu
L
L