Unknown,Transcriptomics,Genomics,Proteomics

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Identification of the PhoB regulon and role of PhoU in the phosphate-starvation response of Caulobacter crescentus (ChIP-seq)

ABSTRACT: An ability to sense and respond to changes in extracellular phosphate is critical to the survival of most bacteria. For Caulobacter crescentus, which typically lives in phosphate-limited environments, this process is especially crucial. Like many bacteria, Caulobacter responds to phosphate limitation through a conserved two-component signaling pathway called PhoR-PhoB, but the direct regulon of PhoB in this organism is unknown. Here, we use ChIP-Seq to map the global binding patterns of the phosphate-responsive transcriptional regulator PhoB in both phosphate-limited and -replete conditions. Combined with genome-wide expression profiling, our work demonstrates that PhoB is induced to regulate nearly 50 genes in phosphate-starved conditions. The PhoB regulon is comprised primarily of genes known or predicted to help Caulobacter scavenge for and import inorganic phosphate, including 15 different membrane transporters. We also investigated the regulatory role of PhoU, a widely conserved protein proposed to coordinate phosphate import with expression of the PhoB regulon by directly modulating the histidine kinase PhoR. However, our studies show that it likely does not play such a role in Caulobacter as depleting PhoU has no significant effect on PhoB-dependent gene expression. Instead, cells lacking PhoU exhibit a striking accumulation of large polyphosphate granules suggesting that PhoU participates in controlling intracellular phosphate metabolism. An allele of phoB bearing a C-terminal 3x-flag tag was integrated at its native locus, and ChIP followed by deep sequencing on Illumina MiSeq was performed on samples grown in rich medium, phosphate-limited medium, and in a pstS::Tn5 mutant background in rich medium.

ORGANISM(S): Caulobacter crescentus NA1000

SUBMITTER: Michael Laub

PROVIDER: E-GEOD-71860 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Identification and characterization of HP1BP3 (a human histone H1 homologue) as a novel chromatin retention factor essential for the co-transcriptional processing of pri-miRNA. We generated BAC transgenic cells at 80% confluency (~1x107) were cross-linked with 1% formaldehyde for 10 minutes at 37Â°C, and quenched with 125 mM glycine at room temperature for 5 minutes. The fixed cells were washed twice with cold PBS, scraped, and transferred into 1 ml PBS containing protease inhibitors (Roche). After centrifugation at 700 g for 4 minutes at 4Â°C, the cell pellets were resuspended in 100 Î¼l ChIP lysis buffer (1% SDS, 10 mM EDTA, 50 mM Tris-HCl [pH 8.1] with protease inhibitors) and sonicated at 4Â°C with a Bioruptor (Diagenode) (30 seconds ON and 30 seconds OFF at highest power for 15 minutes). The sheared chromatin with a fragment length of ~200 â 600 bp) was centrifuged at 20,000 g for 15 minutes at 4Â°C). 100 Î¼l of the supernatant was used for ChIP or as input. A 1:10 dilution of the solubilized chromatin in ChIP dilution buffer (0.01% SDS, 1.1% Triton X-100, 1.2 mM EDTA, 167 mM NaCl 16.7 mM Tris-HCl [pH 8.1]) was incubated at 4Â°C overnight with 6 Î¼g/ml of a goat anti-GFP (raised against His-tagged full-length eGFP and affinity-purified with GST-tagged full-length eGFP). Immunoprecipitation was carried out by incubating with 40 Î¼l pre-cleared Protein G Sepharose beads (Amersham Bioscience) for 1 hour at 4Â°C, followed by five washes for 10 minutes with 1ml of the following buffers: Buffer I: 0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl [pH 8.1], 150 mM NaCl; Buffer II: 0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl [pH 8.1], 500 mM NaCl; Buffer III: 0.25 M LiCl, 1% NP-40, 1% deoxycholate, 1 mM EDTA, 10 mM Tris-HCl [pH 8.1]; twice with TE buffer [pH 8.0]. Elution from the beads was performed twice with 100 Î¼l ChIP elution buffer (1% SDS, 0.1 M NaHCO3) at room temperature (RT) for 15 minutes. Protein-DNA complexes were de-crosslinked by heating at 65Â°C in 192 mM NaCl for 16 hours. DNA fragments were purified using QiaQuick PCR Purification kit (QIAGEN) and eluted into 30 Î¼l H2O according to the manufacturerâs protocol after treatment with RNase A and Proteinase K.

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Identification of the PhoB regulon and role of PhoU in the phosphate-starvation response of Caulobacter crescentus (ChIP-seq)

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