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Control of expression of the ICE R391 encoded UV-inducible cell-sensitising function


Armshaw, Patricia; Pembroke, Tony J;

Institution: BioMed Central
Subject Keywords: type IV secretion system; conjugative transfer; UV-induced sensitisation and cytotoxicity; coli-reca protein; escherichia-coli; plasmid R391; elements; system; irradiation; genome; repair; genes; phage;

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 postirradiation 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 lambda 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.

Suggested citation:

Armshaw, Patricia; Pembroke, Tony J; . () Control of expression of the ICE R391 encoded UV-inducible cell-sensitising function [Online]. Available from: [Accessed: 14th November 2019].


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