lac RepressorThere are four identical subunits that form nine domains. The C-terminus from each subunit forms a four-helix bundle. The helices are almost perfectly anti-parallel to ones of the same color, but form a conventional left-handed coiled-coil with helices of a different color. All leucines are initially colored blue. Then 342 and 349 (i, i+7) in each subunit are changed to cyan.
Friedman AM, Fischmann TO, Steitz TA.Crystal structure of lac repressor core tetramer and its implications for DNA looping. 1tlf PDB file
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