title: Control of expression of the ICE R391 encoded UV-inducible cell-sensitising function.
abstract: BACKGROUND
  Many SXT/R391-like enterobacterial Integrative Conjugative Elements (ICEs) have been found to express an atypical, recA-dependent, UV-inducible, cell-sensitising phenotype observed as a reduction in post-irradiation cell survival rates in host cells. Characterisation of a complete deletion library of the prototype ICE R391 identified the involvement of three core ICE genes, orfs90/91 encoding a putative transcriptional enhancer complex, and orf43, encoding a putative type IV secretion system, outer membrane-associated, conjugative transfer protein.
  
  
  RESULTS
  In this study, expression analysis of orf43 indicated that it was up-regulated as a result of UV irradiation in an orfs90/91-dependent manner. Induced expression was found to be controlled from a site preceding the gene which required functional orfs90/91. Expression of orfs90/91 was in turn found to be regulated by orf96, a λ cI-like regulator. Targeted construction of ICE R391 deletions, RT-PCR and qRT-PCR analysis confirmed a regulatory link between orfs90/91 and orf43 while site-directed mutagenesis of orf43 suggested an association with the cell membrane was a prerequisite for the cytotoxic effect.
  
  
  CONCLUSIONS
  Because of the recA-dependence of the effect, we hypothesise that UV induction of RecA results in cleavage of the cI-like ICE-encoded repressor protein, the product of orf96. This in turn allows expression of the transcriptional enhancer complex encoded by orfs90/91, which we conclude stimulates transcription of orf43, whose product is directly responsible for the effect.
authors.affiliation: Molecular and Structural Biochemistry Laboratory, Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland. tony.pembroke@ul.ie.
authors.forename: Patricia
authors.initials: P
authors.lastname: Armshaw
authors.forename: J Tony
authors.initials: JT
authors.lastname: Pembroke
mesh_terms: D058947:Bacterial Secretion Systems / Q000235:genetics*; D004252:DNA Mutational Analysis; D004755:Enterobacteriaceae / Q000502:physiology / Q000528:radiation effects*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects*; D020071:Interspersed Repetitive Sequences; D050296:Microbial Viability / Q000528:radiation effects*; D060888:Real-Time Polymerase Chain Reaction; D011938:Rec A Recombinases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D058947:Bacterial Secretion Systems; D014157:Transcription Factors; D011938:Rec A Recombinases