Suppression of transcription polarity in the Escherichia coli haemolysin operon by a short upstream element shared by polysaccharide and DNA transfer determinants

Abstract

Expression of the Escherichia coli hlyCABD operon encoding synthesis, maturation and export of haemolysin toxin was strongly dependent upon a 35 bp DNA sequence, spanning the element GGCGGTAG, located 2 kbp upstream. When the hly operon was placed under the control of the inducible tac promoter, expression remained dependent upon this element, when transcribed in its native orientation 3' of the promoter. The increase in ptac-directed transcription was strongest for the distal, export genes of the hly operon, and was particularly striking when ptac and the element were placed far upstream. The element did not influence transcript stability, and we suggest that it is a key component of a novel regulatory mechanism may suppresses transcription polarity within operons. The mechanism that be of widespread importance in bacterial gene expression because the 8 bp element is present in many Gram-negative species as an upstream component of operons encoding the production of toxins and the surface assembly of polysaccharides and components required for the conjugal transfer of DNA. We name it the ops element for operon polarity suppressor.

O-antigen expression in Salmonella enterica serovar Typhi is regulated by nitrogen availability through RpoN-mediated transcriptional control of the rfaH gene

“…Evidence from other studies has demonstrated that the transcription of the LPS core and O-polysaccharide gene clusters is subject to positive regulation at the level of mRNA elongation by the RfaH protein (Farewell et al, 1991 ;Pradel & Schnaitman, 1991 ;Bailey et al, 1996 ;Marolda & Valvano, 1998 ; targeted to the cell surface or membrane (Bailey et al, 1997) by promoting the efficient elongation of the mRNA (Artsimovitch & Landick, 2002). Based on a detailed deletion-fusion analysis of the E. coli O7 LPS promoter region, Marolda & Valvano (1998) have proposed a model involving premature termination of transcription relieved by the RfaH protein that operates to regulate the expression of O-specific polysaccharide genes.…”

“…RfaH is a homologue of the NusG factor that regulates gene expression of the haemolysin operon (Bailey et al, 1992 ;Leeds & Welch, 1996, polysaccharide capsule genes (Stevens et al, 1997), the F plasmid tra operon (Beutin & Achtman, 1979), and a gene involved in iron acquisition (Nagy et al, 2001). RfaH regulation occurs during transcript elongation and depends on a 5h-proximal, transcribed nucleic acid sequence known as ops (for operon polarity suppressor ; Nieto et al, 1996 ;Bailey et al, 1997) that induces transcriptional pausing in vitro (Artsimovitch & Landick, 2000) and in vivo (Leeds & Welch, 1997). It has been recently demonstrated that RfaH recognizes RNApolymerase transcribing RfaH-regulated operons by interacting with the ops sequence in the exposed nontemplate DNA strand of ops-paused transcription complexes (Artsimovitch & Landick, 2002).…”

Analysis of the wee gene cluster responsible for the biosynthesis of the polymeric bioemulsifier from the oil-degrading strain Acinetobacter lwoffii RAG-1 The GenBank/EMBL accession number for the sequence analysis of the eight fragments determined in this work is AJ243431.

“…promoter sequences within this non-translated region in both upstream and downstream directions. Interestingly, no sequence was found which corresponded to the 39 bp JUMPstart element generally located upstream of polysaccharide biosynthetic gene clusters (Hobbs & Reeves, 1994) nor for the 8 bp ops elements normally present within the JUMPstart sequences which are thought to function in antitermination of transcription (Bailey et al, 1997 ;Nieto et al, 1996). One region, transcribed in the upstream direction, appears to encode 3 complete ORFs, while the second region is transcribed in the opposite direction and encodes 17 complete ORFs (Fig.…”

An Escherichia coli gene (yaeO ) suppresses temperature‐sensitive mutations in essential genes by modulating Rho‐dependent transcription termination

“…These include bacteriophage Q and N-dependent anti-termination (reviewed by Greenblatt et al, 1993;Richardson and Greenblatt, 1996), NusBAG-S10-dependent anti-termination at ribosomal operons (reviewed by Condon et al, 1995) and RfaH-dependent anti-termination at operons involved in toxin production, polysaccharide assembly and conjugal transfer of DNA (Leeds and Welch, 1996;Nieto et al, 1996). All these anti-termination systems result from a specific sequence in the 5Ј region of the transcript that loads an anti-termination factor and modifies the susceptibility of RNA polymerase to factor Rho.…”