Abstract:
: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.
journal_name
Proc Natl Acad Sci U S Aauthors
Kania J,Brown DTdoi
10.1073/pnas.73.10.3529subject
Has Abstractpub_date
1976-10-01 00:00:00pages
3529-33issue
10eissn
0027-8424issn
1091-6490journal_volume
73pub_type
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