1TLF

UNPRECEDENTED QUATERNARY STRUCTURE OF E. COLI LAC REPRESSOR CORE TETRAMER: IMPLICATIONS FOR DNA LOOPING

Summary for 1TLF

• Entry DOI: 10.2210/pdb1tlf/pdb
• Descriptor: LAC REPRESSOR, ETHYL MERCURY ION, 1-methylethyl 1-thio-beta-D-galactopyranoside (3 entities in total)
• Functional Keywords: transcription regulation
• Biological source: Escherichia coli
• Total number of polymer chains: 4
• Total formula weight: 130490.58

Authors

Friedman, A.M.,Fischmann, T.O.,Steitz, T.A. (deposition date: 1995-03-06, release date: 1995-07-31, Last modification date: 2024-02-14)

Primary citation

Friedman, A.M.,Fischmann, T.O.,Steitz, T.A.
Crystal structure of lac repressor core tetramer and its implications for DNA looping.
Science, 268:1721-1727, 1995

PubMed Abstract: The crystal structure of the tryptic core fragment of the lac repressor of Escherichia coli (LacR) complexed with the inducer isopropyl-beta-D-thiogalactoside was determined at 2.6 A resolution. The quaternary structure consists of two dyad-symmetric dimers that are nearly parallel to each other. This structure places all four DNA binding domains of intact LacR on the same side of the tetramer, and results in a deep, V-shaped cleft between the two dimers. Each monomer contributes a carboxyl-terminal helix to an antiparallel four-helix bundle that functions as a tetramerization domain. Some of the side chains whose mutation reduce DNA binding form clusters on a surface near the amino terminus. Placing the structure of the DNA binding domain complexed with operator previously determined by nuclear magnetic resonance onto this surface results in two operators being adjacent and nearly parallel to each other. Structural considerations suggest that the two dimers of LacR may flexibly alter their relative orientation in order to bind to the known varied spacings between two operators.

PubMed: 7792597

Experimental method

X-RAY DIFFRACTION (2.6 Å)