Kania J, Brown D T
Proc Natl Acad Sci U S A. 1976 Oct;73(10):3529-33. doi: 10.1073/pnas.73.10.3529.
The chimaeric protein repressor-galactosidase, in which fully active lac repressor is covalently linked to the active enzyme beta-galactosidase, was used as a system for probing the quaternary structure of lac repressor. Electron micrographs revealed repressor-galactosidase to be a tetrameric aggregate. When lac repressor, alone, was crosslinked with dimethyl suberimidate, dimers, trimers, tetramers, and oligomers of the protein subunit were produced, whereas crosslinking of the tetrameric repressor-galactosidase resulted in the production of only dimers of the chimaera. Treatment of lac repressor with iodine resulted in the formation of protein dimers; the same result was obtained with repressor-galactosidase. After limited proteolysis of lac repressor, no crosslinking was obtained after treatment with dimethyl suberimidate, whereas iodine still produced a covalent linkage. These results are interpreted as evidence that the lac repressor parts of the tetrameric repressor-galactosidase-chimaera are organized as dimers on the tetrameric-beta-galactosidase core. Because this chimaera has been previously shown to have normal repressor activity [B. Müller-Hill and J. Kania (1974) Nature, 249,561-563], we conclude that lac repressor still is biologically active as a dimeric aggregate.
嵌合蛋白阻遏物 - 半乳糖苷酶是将完全活性的乳糖阻遏物与活性酶β - 半乳糖苷酶共价连接而成，被用作探究乳糖阻遏物四级结构的系统。电子显微镜照片显示阻遏物 - 半乳糖苷酶是一种四聚体聚集体。当单独的乳糖阻遏物与亚胺基二甲酯交联时，会产生蛋白质亚基的二聚体、三聚体、四聚体和寡聚体，而四聚体的阻遏物 - 半乳糖苷酶交联后仅产生嵌合体的二聚体。用碘处理乳糖阻遏物会导致蛋白质二聚体的形成；阻遏物 - 半乳糖苷酶也得到相同结果。对乳糖阻遏物进行有限蛋白酶解后，用亚胺基二甲酯处理后未获得交联产物，而碘仍能产生共价连接。这些结果被解释为表明四聚体阻遏物 - 半乳糖苷酶 - 嵌合体中的乳糖阻遏物部分在四聚体β - 半乳糖苷酶核心上以二聚体形式组织。因为此前已证明这种嵌合体具有正常的阻遏物活性[B. 米勒 - 希尔和J. 卡尼亚（1974年）《自然》，249,561 - 563]，所以我们得出结论，乳糖阻遏物作为二聚体聚集体仍具有生物学活性。
