Lipp J, Dobberstein B
J Cell Biol. 1986 Jun;102(6):2169-75. doi: 10.1083/jcb.102.6.2169.
Invariant (Ii) chain is a membrane-spanning protein that is found associated intracellularly with class II histocompatibility antigens. In the endoplasmic reticulum Ii chain spans the membrane and exposes the NH2 terminus on the cytoplasmic and the COOH terminus on the lumenal side. This orientation across the membrane is demonstrated directly with the monoclonal antibody In-1, which exclusively recognizes the NH2 terminal cytoplasmically exposed part of Ii chain. Membrane insertion of Ii chain requires signal recognition particle and docking protein. When tested in a wheat germ cell free system, signal recognition particle arrests translation of Ii chain. No signal sequence is cleaved from Ii chain upon membrane insertion.
恒定链(Ii链)是一种跨膜蛋白,在细胞内与Ⅱ类组织相容性抗原相关联。在内质网中,Ii链跨膜,其氨基末端暴露于细胞质一侧,羧基末端暴露于腔一侧。通过单克隆抗体In-1可直接证明Ii链在膜上的这种取向,该抗体专门识别Ii链氨基末端在细胞质中暴露的部分。Ii链插入膜需要信号识别颗粒和对接蛋白。在麦胚无细胞系统中进行测试时,信号识别颗粒会阻止Ii链的翻译。Ii链插入膜时不会切割信号序列。