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RNAs binding to the nucleoid protein HU in Escherichia coli

ABSTRACT: HU is a conserved prokaryotic nucleoid-associated protein known for its role in DNA binding and maintaining negative supercoils in DNA. HU also binds to a few RNAs but the natural targets are unknown. To understand the biology of HU interactions with RNA in Escherichia coli, potential HU-RNA in vivo complexes were immunoprecipitated and bound RNAs were examined by hybridization to whole-genome tiling arrays. We observed HU associations with rRNA, multiple tRNAs, a few sRNAs and a small, distinct set of mRNAs. More importantly, we also identified associations between HU and ten intragenic non-coding (nonc) RNAs, two of which are homologous to the annotated Bacterial Interspersed Mosaic Elements (BIME) and boxC elements; the other eight RNAs have not been annotated. We confirmed binding of HU to BIME RNA in vitro. Since HU and some unidentified RNAs have been implicated in the nucleoid structure, we explored an idea that HU, along with some or all of the nonc RNA species discovered here bind to BIME and/or boxC repeats to condense chromosomal DNA in a specific fashion. We propose that nonc RNAs may interact with both HU and DNA repeats to form ternary complexes, which are the anchoring points separating different chromosomal domains.

ORGANISM(S): Escherichia coli

PROVIDER: GSE28565 | GEO | 2012/12/07

SECONDARY ACCESSION(S): PRJNA139137

REPOSITORIES: GEO

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Project description:Nucleoid remodeling facilitated by DNA supercoiling results in changes in nucleoid configuration and involves nucleoid-associated proteins (NAPs) and structural maintenance of chromosomes (SMC) proteins among others. Changes in nucleoid configurations regulated by NAPs are synchronized with cellular adaptation and influence the simultaneous expression of several genes. HU, a ubiquitous bacterial histone-like protein, is among the most conserved and abundant NAPs in eubacteria. In Escherichia coli, HU forms dimers by HUα self-association (HUαα) or by HUα-HUβ interactions (HUαβ). HUα is mostly expressed during lag and early exponential growth phase and HUβ is expressed only during the later exponential and stationary phase, pointing to distinct HUαα/DNA and HUαβ/DNA packaging of the nucleoid in regulating expression patterns during growth and stasis. Mutations or the deletion of HU transform the E. coli nucleoid to a different form and alter overall transcription program; thus, HU interactions with DNA directly affect global gene regulation. Recently, analysis of high-resolution contact maps of the E. coli nucleoid revealed an important role of HU to promote long-range DNA-DNA contacts within the nucleoid. Yet, the molecular connections between HU-DNA interactions and changes in nucleoid architecture that regulate gene expression globally remain unknown. Here, we explored the higher-order E. coli nucleoid organization by soft x-ray tomography (SXT) and revealed an effect of HU surface charges in overall nucleoid organization and rearrangements. We also studied global transcription by next-generation RNA sequencing (RNA-Seq) and found a link between nucleoid rearrangement and changes in global transcription. To determine the functional relationships of observed nucleoid rearrangement and HU-DNA interactions, we also characterized the overall organization of HU nucleoprotein complexes in solution by small angle x-ray scattering (SAXS). We found that HUαα-mediated DNA networks are different at different ionic strengths and pHs. By means of macromolecular crystallography, we additionally elucidate HUαα dependent molecular switches that modulate DNA networking. This integrative structural study explains how HUαα regulates dynamic transformations of the nucleoid by DNA bridging to control nucleoid rearrangement and global gene regulation.

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RNAs binding to the nucleoid protein HU in Escherichia coli

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