Tn5 transposition in Escherichia coli is repressed by Hfq and activated by over-expression of the small non-coding RNA SgrS.

Joseph A Ross,Ryan S Trussler,Crystal R Mclellan,Morgan D Black,David B Haniford

doi:10.1186/s13100-014-0027-z

Abstract

BackgroundHfq functions in post-transcriptional gene regulation in a wide range of bacteria, usually by promoting base pairing of mRNAs with trans-encoded sRNAs. It was previously shown that Hfq down-regulates Tn10 transposition by inhibiting IS10 transposase expression at the post-transcriptional level. This provided the first example of Hfq playing a role in DNA transposition and led us to ask if a related transposon, Tn5, is similarly regulated.ResultsWe show that Hfq strongly suppresses Tn5 transposition in Escherichia coli by inhibiting IS50 transposase expression. However, in contrast to the situation for Tn10, Hfq primarily inhibits IS50 transposase transcription. As Hfq does not typically function directly in transcription, we searched for a transcription factor that also down-regulated IS50 transposase transcription and is itself under Hfq control. We show that Crp (cyclic AMP receptor protein) fits these criteria as: (1) disruption of the crp gene led to an increase in IS50 transposase expression and the magnitude of this increase was comparable to that observed for an hfq disruption; and (2) Crp expression decreased in hfq−. We also demonstrate that IS50 transposase expression and Tn5 transposition are induced by over-expression of the sRNA SgrS and link this response to glucose limitation.ConclusionsTn5 transposition is negatively regulated by Hfq primarily through inhibition of IS50 transposase transcription. Preliminary results support the possibility that this regulation is mediated through Crp. We also provide evidence that glucose limitation activates IS50 transposase transcription and transposition.Electronic supplementary materialThe online version of this article (doi:10.1186/s13100-014-0027-z) contains supplementary material, which is available to authorized users.

Highlights

Hfq functions in post-transcriptional gene regulation in a wide range of bacteria, usually by promoting base pairing of mRNAs with trans-encoded small RNAs (sRNA)
We performed a complementation assay in the DBH179 strain background to further test that the increase in transposition reported above in hfq− was due to the absence of Hfq, as opposed to possible polar effects of the hfq disruption allele
We show that Tn5 transposition and IS50 transposase expression are repressed by Hfq; the mechanism of repression is atypical for Hfq, involving predominantly a block in IS50 transposase transcription

Summary

Introduction

Hfq functions in post-transcriptional gene regulation in a wide range of bacteria, usually by promoting base pairing of mRNAs with trans-encoded sRNAs. It was previously shown that Hfq down-regulates Tn10 transposition by inhibiting IS10 transposase expression at the post-transcriptional level This provided the first example of Hfq playing a role in DNA transposition and led us to ask if a related transposon, Tn5, is regulated. Transposase proteins catalyze the chemical steps in bacterial transposition reactions It follows that the regulation of expression of these genes is a critical feature in dictating the transposition frequency of most transposons. DNA adenine methylase (DAM) limits initiation of IS10 and IS50 transposase gene transcription by methylating promoter elements [1,2] These factors together make transcription initiation a limiting step in Tn10/IS10 and Tn5/IS50 transposition reactions [3,4]. There are examples where translation of transposase transcripts is subject to both intrinsic and host levels of

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