Objective: To research the functional segments of B-FA molecule binding invariant chain and their characters. Methods:The DNA segments (α1α2, sα1α2 and α3TC ) of B-FA genes were respectively cloned and inserted into prokaryotic or eukaryotic expression plasmids,then they were singly or co-transfected with Ii gene into the engineering bacteria E. coli (BL-21)or 293T cells. After induction of expression,affinity chromatography and SDS-PAGE identification,the binding between B-FA segments and Ii molecule and co-localization in cells were observed with Pull-down and Western blot. Results:First three recombinant prokaryotic expression plasmids and four recombinant eukaryotic expression plasmids were constructed. The single molecules expressed by B-FA segments were observed after an affinity chromatography. Secondly the complexes of Ii/B-FA-α1α2 and Ii/B-FA-sα1α2 were detected by a Pull-down from the co-transfected corresponding prokaryotic expression plasmids,but no complex of Ii andα3TC,also in the western blot it was detected that B-FA-α1α2 or B-FA-sα1α2 as functional segment could bind Ii to form complex. Finally in eukaryotic expression 293T cells B-FA-sα1α2 kept localization, the same as B-FA. Conclusion: Chicken B-FA-α1α2 is function segment to bind with Ii molecule and keeps the location characters same as B-FA. The results of this research first time provide experimental evidence about B-FA functional region binding segment to Ii molecule.%目的：：研究鸡Ii链结合的B-FA分子的功能片段及其特征。方法：将克隆的B-FA基因片段(α1α2、sα1α2和α3TC)分别插入原核或真核表达质粒,然后分别转染或与Ii共转染工程菌E. coli(BL-21)或293T细胞,经过诱导表达、亲和层析纯化和SDS-PAGE鉴定后,分别用Pull-down法观察B-FA片段与Ii结合与在细胞内的共定位特征。结果：首先,构建了3个重组原核表达质粒和4个重组真核表达质粒。原核表达的B-FA片段经亲和层析纯化可获得单一蛋白分子。其次,用Pull-down从共转染工程菌表达的蛋白分子中分别检测到Ii/B-FA-α1α2和Ii/B-FA-sα1α2,而未能检测到Ii与α3TC的结合物,而免疫印迹结果也表明该两片段是结合Ii链形成复合物的功能片段。最后,在真核表达的293T中,B-FA-α1α2具有同B-FA相同的细胞定位特性。结论：鸡B-FA-α1α2片段是结合Ii的功能片段,并保持了B-FA的细胞定位的作用。本研究结果首次提供了B-FA分子与Ii的互相作用的实验依据。
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