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#AraC protein

2 public questions tagged with this topic.

Gene regulation in Prokaryotes

In absence of arabinose, AraC binds to

Without L-arabinose, AraC apoprotein adopts conformation strongly promoting looping-mediated repression of araBAD operon. Dimer bridges high-affinity araO2 site centered approximately minus 280 upstream and araI1 site at minus 106, with intervening 210 base pairs bent into looped architecture demonstrated by electron microscopy. Crystallographic studies show N-terminal arms dimerize antiparallel, stabilizing loop topology. Looped conformation buries PBAD minus35 promoter element and occludes CAP-cAMP binding site, preventing RNA polymerase holoenzyme initiation. Approximately twenty AraC molecules per bacterial cell suffice to maintain tight repression, ensuring low basal expression until arabinose reaches threshold concentration sufficient to disrupt loop architecture.

Ref: Science DNA Looping by AraC – apo-AraC prefers looping between araO2 and araI1 repressing araBAD.

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Gene regulation in Prokaryotes

AraC protein functions as

AraC protein embodies remarkable dual regulatory function determined by arabinose-dependent conformational switch. Polypeptide of 292 residues contains N-terminal dimerization and arabinose-binding domain linked via flexible interdomain arm to C-terminal DNA-binding domain possessing two helix-turn-helix motifs. Apo form without arabinose favors interaction binding to distal O2 operator and I1 half-site forming DNA repression loop that blocks polymerase. Arabinose-bound form reorganizes N-terminal arm, neutralizes arm dimer interactions, shifts DNA-binding specificity to adjacent I1-I2 half-sites upstream of PBAD, and exposes activation surface capable of direct contacts with RNA polymerase alpha subunit, behaving simultaneously as both repressor and activator depending on ligand status.

Ref: L-arabinose operon review – AraC is dual activator-repressor; apo-AraC loops araI1-O2 (210 bp) to repress.

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