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Two-level inhibition of galK expression by Spot 42: Degradation of mRNA mK2 and enhanced transcription termination before the galK gene
- Wang, Xun, Ji, Sang Chun, Jeon, Heung Jin, Lee, Yonho, Lim, Heon M.
- Proceedings of the National Academy of Sciences of the United States of America 2015 v.112 no.24 pp. 7581-7586
- Escherichia coli, messenger RNA, operon
- The Escherichia coli gal operon has the structure Pgal-galE-galT-galK-galM . During early log growth, a gradient in gene expression, named type 2 polarity, is established, as follows: galE > galT > galK > galM . However, during late-log growth, type 1 polarity is established in which galK is greater than galT , as follows: galE > galK > galT > galM . We found that type 2 polarity occurs as a result of the down-regulation of galK , which is caused by two different molecular mechanisms: Spot 42-mediated degradation of the galK- specific mRNA, mK2, and Spot 42-mediated Rho-dependent transcription termination at the end of galT . Because the concentration of Spot 42 drops during the transition period of the polarity type switch, these results demonstrate that type 1 polarity is the result of alleviation of Spot 42-mediated galK down-regulation. Because the Spot 42-binding site overlaps with a putative Rho-binding site, a molecular mechanism is proposed to explain how Spot 42, possibly with Hfq, enhances Rho-mediated transcription termination at the end of galT .