title: Expression of each cistron in the gal operon can be regulated by transcription termination and generation of a galk-specific mRNA, mK2.
abstract: The gal operon of Escherichia coli has 4 cistrons, galE, galT, galK, and galM. In our previous report (H. J. Lee, H. J. Jeon, S. C. Ji, S. H. Yun, H. M. Lim, J. Mol. Biol. 378: 318-327, 2008), we identified 6 different mRNA species, mE1, mE2, mT1, mK1, mK2, and mM1, in the gal operon and mapped these mRNAs. The mRNA map suggests a gradient of gene expression known as natural polarity. In this study, we investigated how the mRNAs are generated to understand the cause of natural polarity. Results indicated that mE1, mT1, mK1, and mM1, whose 3' ends are located at the end of each cistron, are generated by transcription termination. Since each transcription termination is operating with a certain frequency and those 4 mRNAs have 5' ends at the transcription initiation site(s), these transcription terminations are the basic cause of natural polarity. Transcription terminations at galE-galT and galT-galK junctions, making mE1 and mT1, are Rho dependent. However, the terminations to make mK1 and mM1 are partially Rho dependent. The 5' ends of mK2 are generated by an endonucleolytic cleavage of a pre-mK2 by RNase P, and the 3' ends are generated by Rho termination 260 nucleotides before the end of the operon. The 5' portion of pre-mK2 is likely to become mE2. These results also suggested that galK expression could be regulated through mK2 production independent from natural polarity.
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Republic of Korea.
authors.forename: Xun
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Republic of Korea.
authors.forename: Sang Chun
authors.initials: SC
authors.lastname: Ji
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Republic of Korea.
authors.forename: Sang Hoon
authors.initials: SH
authors.lastname: Yun
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Republic of Korea.
authors.forename: Heung Jin
authors.initials: HJ
authors.lastname: Jeon
authors.affiliation: Department of Environmental Engineering, Pioneer Research Center for Controlling of Harmful Algal Blooming, Chosun University, Gwangju, Republic of Korea.
authors.forename: Si Wouk
authors.initials: SW
authors.lastname: Kim
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Republic of Korea hmlim@cnu.ac.kr.
authors.forename: Heon M
authors.initials: HM
authors.lastname: Lim
mesh_terms: D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005686:Galactokinase / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial / Q000502:physiology; D009876:Operon / Q000235:genetics*; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D061806:Transcription Termination, Genetic / Q000502:physiology*
chemical_list: D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D005686:Galactokinase; D004722:Endoribonucleases; C022537:ribonuclease E