Ko K, Budd D, Wu C, Seibert F, Kourtz L, Ko Z W
Department of Biology, Queen's University, Kingston, Ontario, Canada.
J Biol Chem. 1995 Dec 1;270(48):28601-8. doi: 10.1074/jbc.270.48.28601.
Many of the proteins in the chloroplast envelope play an important role in facilitating the biochemical and transport processes of the compartment. For the transport of proteins into the chloroplast, we have recently identified at least three different envelope proteins (Com44/Cim44, Com70, and Cim97) in close physical proximity to a partially translocated chimeric precursor protein (Wu, C., Seibert, F. S., and Ko, K. (1994) J. Biol. Chem. 269, 32264-32271). In this study we report the characterization of a cDNA clone encoding a member of the Com44/Cim44 envelope proteins. The combined data from nucleotide sequencing, and RNA and protein blot analyses indicate the existence of multiple forms of the 44-kDa envelope protein. Depending on the plant species examined, immunologically-related protein bands with molecular masses of 42 to 46 kDa were observed. Organelle subfractionation, protease treatment, and immunomicroscopic studies together provide an indication that the immunologically-related proteins may be present in both the outer and inner envelope membranes. Co-migration of the product synthesized from the cDNA insert with a 44-kDa immunoreactive band of the chloroplast envelope, and the in vitro import results, together suggest that the in vitro synthesized 44-kDa protein is targeted to the envelope membrane without any further processing.
叶绿体被膜中的许多蛋白质在促进该细胞器的生化和运输过程中发挥着重要作用。对于蛋白质运输到叶绿体的过程，我们最近在物理位置上与一种部分转运的嵌合前体蛋白紧密相邻处鉴定出了至少三种不同的被膜蛋白（Com44/Cim44、Com70和Cim97）（Wu, C., Seibert, F. S., and Ko, K. (1994) J. Biol. Chem. 269, 32264 - 32271）。在本研究中，我们报告了一个编码Com44/Cim44被膜蛋白成员的cDNA克隆的特征。来自核苷酸测序、RNA和蛋白质印迹分析的综合数据表明存在多种形式的44 kDa被膜蛋白。根据所检测的植物物种，观察到分子量为42至46 kDa的免疫相关蛋白条带。细胞器亚分级分离、蛋白酶处理和免疫显微镜研究共同表明，免疫相关蛋白可能存在于外被膜和内被膜中。由cDNA插入片段合成的产物与叶绿体被膜的44 kDa免疫反应条带共迁移，以及体外导入结果共同表明，体外合成的44 kDa蛋白无需任何进一步加工即可靶向被膜。
