DNA looping and Lac repressor CAP interaction
DNA looping and Lac repressor CAP interaction
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DOI：
10.1126/science.274.5294.1930
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发表时间：
1996-12-13
期刊：
影响因子：
56.9
通讯作者：
Hudson, JM
中科院分区：
文献类型：
--
作者：
Fried, MG;Hudson, JM
ranoside (IPTG) provide highly detailed views of molecular interactions that control the lac system (1). These structures also provide a rational basis for the construction of models of regulatory complex-es that contain additional proteins. In one such model, proposed by Lewis and his colleagues, a lac repressor tetramer forms a bridge between operator sites 01 and 03, and the intervening DNA (approximately 90 bp) forms a smoothly curved loop. The structure of the transcription activator protein (CAP) complex with bent DNA, determined by Schultz et al.(2), was built into Lewis et al.'s model, with its DNA occupying the position corresponding to the principal CAP site (Cl) of the lac promoter. Lewis et al.'s model accounts, in principle, for the enhanced repression of lac transcription observed when templates contain site 03 as well as 0 (3). Al-though a role for CAP in this effect has yet to be shown, its ability to bend DNA by 90 配 o 1300 (2, 4) makes its inclusion plausible.Lewis et al.'s model requires the simul-taneous binding of site Cl by CAP and of 03 by repressor, with the proteins occupying opposite faces of the DNA helix. Data currently in the literature appear to argue against this. First, when CAP and repressor bind independently, their sites, defined by DNase I protection, overlap by approxi-mately 9 bp [(5); compare also Fig. 1, lanes c and g]. Second, the center-to-center sep-aration of these sites is only 20.5 bp [see, for example (6, 7)]. If the intervening DNA is B-form, both proteins should occupy the same face of the helix. These results predict steric clash between CAP and repressor that might prevent simultaneous binding