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GalR mediated interactions in the E. coli chromosome

Tuesday, October 25, 2011 — Poster Session II

Noon – 2:00 p.m.

Natcher Conference Center




  • Z Qian
  • EK Dimitriadis
  • S Adhya


It has been reported that dimerized GalR could bind to 7 sites along the E.coli chromosome to regulate gene expression. Here, we label GalR at the C terminus with Venus fluorescent protein, for single molecule detection in E.coli. In cells growing in stationary phase, 2 or 3 fluorescence spots per cell (55% and 31%) were detected regardless of the presence or absence of galactose. In log phase, however, we could not observe any similar spots. Furthermore, GalR mutations inhibiting tetramer formation abolished the spots also in stationary phase. We propose that GalR that binds to operator sites could polymerize and facilitate long distance looping. To examine this, we employed Atomic Force Microscopy (AFM) and Chromosome Conformation Capture (3C) analysis. By AFM we visualize GalR binding and consequent DNA looping. Analysis of the loop sizes identifies operator pairs bound via GalR oligomers and quantifies the cooperativity that brings distant operators together. A 3C analysis suggests that DNA targets of GalR distributed around the chromosome, are connected with one another mostly in stationary phase cells, a connection that is lost in the log phase. Furthermore, we identified five additional potential bindings of GalR along the investigated region.

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