What is it about?

Four structural genes, galE, T, K, and M constitute the multi-cistronic gal operon in E. coli. The gal operon produces 4 mRNAs, mE1, mT1, mK1, and mM1, smaller than the full-length mRNA. The 5' end of the 4 mRNAs reside at the transcription initiation site, and the 3' ends are at the end of the corresponding gene. Thus, production of these mRNAs establishes what has been known as polarity in gene expression; higher in a gene closer to the promoter. We measured the efficiency of Rho-mediated transcription termination at the end of each gene. It is 16, 29, 65 and 71 % at the end of galE, T, K, and M, respectively. The operon produces another mRNA, mK2, that has its 5' end at the beginning of the galT gene and 3' end at the end of the operon. Thus, mK2 production would act against polarity, because mK2 production would increase the expression of galK which is distal to the promoter.

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Why is it important?

Each cistron junction of the gal operon has unique structure. The Rho-mediated transcription termination at the end of each cistron has specific termination efficiency. In E. coli, a break in the coupled transcription-translation status leads to Rho-termination. These results suggest that translation termination and initiation at each cistron junction has a unique role in Rho-termination, raising a possibility that the E. coli cells can control expression of each gene in gal operon by regulating transcription-translation coupling status at each cistron junction. E. coli cells could gain a control of the galK expression independently by controlling mK2 production presumably through a small RNA Spot 42.

Perspectives

I think the result from this publication would lead to a discovery of how Rho-termination occurs at each cistron junction.

Professor Heon M. Lim
Chungnam National University

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This page is a summary of: Expression of Each Cistron in the gal Operon Can Be Regulated by Transcription Termination and Generation of a galK-Specific mRNA, mK2, Journal of Bacteriology, May 2014, ASM Journals,
DOI: 10.1128/jb.01577-14.
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