title: Rem, a new transcriptional activator of motility and chemotaxis in Sinorhizobium meliloti.
abstract: The expression of 51 known genes clustered in the flagellar regulon of Sinorhizobium meliloti is organized as a three-class hierarchy: class IA comprises the master regulatory genes, visN and visR; class II, controlled by VisNR, comprises flagellar assembly and motility genes; and class III comprises flagellin and chemotaxis genes requiring class II for expression. The expression of visN-visR is constitutive throughout growth, whereas that of class II and class III genes is limited to exponential growth. A new OmpR-like, 25-kDa transcription factor, Rem, whose synthesis is confined to exponential growth, was shown to positively control swimming motility. No phosphorylation of the receiver domain of Rem was required for its activity. Gene expression in tester strains with known deficiencies placed the rem gene (class IB) below visN-visR (class IA) and above class II genes in the regulatory cascade. Footprinting analysis demonstrated that the Rem protein binds to class II gene promoters as well as to its own promoter, indicating that this protein is autoregulatory. An alignment of the Rem-protected DNA sequences revealed a conserved binding motif of imperfect tandem repeats overlapping a predicted -35 promoter box by 3 bp. This new promoter was confirmed by mapping the transcription start site of a typical class II gene, flgB, 5 nucleotides downstream of the -10 promoter box. The transcription of rem is under dual control of an upstream (Rem-activated) class II-type promoter and a downstream (VisNR-activated) sigma70-like promoter. The central role of Rem as the growth-dependent transcriptional activator intermediate between the master regulator, VisNR, and the flagellar and motility genes is a new distinguishing feature of the S. meliloti regulatory cascade.
authors.affiliation: Institute of Biochemistry, Genetics and Microbiology, University of Regensburg, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Rotter
authors.forename: Susanne
authors.initials: S
authors.lastname: Mühlbacher
authors.forename: Daniel
authors.initials: D
authors.lastname: Salamon
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Schmitt
authors.forename: Birgit
authors.initials: B
authors.lastname: Scharf
mesh_terms: D000595:Amino Acid Sequence; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002633:Chemotaxis / Q000235:genetics*; D018983:DNA Footprinting; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D008954:Models, Biological; D008969:Molecular Sequence Data; D009068:Movement; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000502:physiology*; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D024363:Transcription Initiation Site; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D015534:Trans-Activators; D001616:beta-Galactosidase