title: Two-level inhibition of galK expression by Spot 42: Degradation of mRNA mK2 and enhanced transcription termination before the galK gene.
abstract: 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.
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon 305-764, 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 305-764, 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 305-764, Republic of Korea.
authors.forename: Heung Jin
authors.initials: HJ
authors.lastname: Jeon
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon 305-764, Republic of Korea.
authors.forename: Yonho
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Department of Biological Sciences, College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon 305-764, Republic of Korea hmlim@cnu.ac.kr.
authors.forename: Heon M
authors.identifier: http://orcid.org/0000-0003-1711-2589
authors.initials: HM
authors.lastname: Lim
mesh_terms: D001483:Base Sequence; D015536:Down-Regulation; D048168:Escherichia coli K12 / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D005686:Galactokinase / Q000235:genetics* / Q000378:metabolism*; D005690:Galactose / Q000378:metabolism; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D035001:Host Factor 1 Protein / Q000378:metabolism; D008969:Molecular Sequence Data; D009876:Operon; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D061806:Transcription Termination, Genetic
chemical_list: D029968:Escherichia coli Proteins; C087373:Hfq protein, E coli; D035001:Host Factor 1 Protein; D012329:RNA, Bacterial; D012333:RNA, Messenger; C534627:Rho protein, E coli; D005700:Galactosyltransferases; D005686:Galactokinase; D005690:Galactose
keywords: Rho-termination; Spot 42; galactose operon; sRNA; target mRNA degradation