Global DNA Compaction in Stationary-Phase Bacteria Does Not Affect Transcription.

In stationary-phase Escherichia coli, Dps (DNA-binding protein from starved cells) is the most abundant protein component of the nucleoid. Dps compacts DNA into a dense complex and protects it from damage. Dps has also been proposed to act as a global regulator of transcription. Here, we directly examine the impact of Dps-induced compaction of DNA on the activity of RNA polymerase (RNAP). Strikingly, deleting the dps gene decompacted the nucleoid but did not significantly alter the transcriptome and only mildly altered the proteome during stationary phase. Complementary in vitro assays demonstrated that Dps blocks restriction endonucleases but not RNAP from binding DNA. Single-molecule assays demonstrated that Dps dynamically condenses DNA around elongating RNAP without impeding its progress. We conclude that Dps forms a dynamic structure that excludes some DNA-binding proteins yet allows RNAP free access to the buried genes, a behavior characteristic of phase-separated organelles.

Impact of pre-existing background therapy on placebo responses in randomised controlled clinical trials of rheumatoid arthritis.

OBJECTIVES: Various hypotheses exist for the explanation of placebo response rates in randomised controlled trials (RCTs) of patients with rheumatoid arthritis with IR to methotrexate (MTX). We hypothesised that placebo responses may be related to more consequent intake of MTX during the tightly monitored trial period. METHODS: We conducted a post hoc analysis of placebo-treated patients included in two RCTs that had allowed inclusion of patients with and without ongoing MTX: the GO-AFTER and the SIRROUND-T trials. We pooled placebo patients of both trials and compared American College of Rheumatology (ACR) 20%/50%/70% response rates and Clinical Disease Activity Index (CDAI) low disease activity (LDA; ie, CDAI ≤10) responses between those receiving placebo on top of continued MTX and those receiving placebo without any background disease modifying antirheumatic drugs (DMARDs). RESULTS: Of 398 placebo patients, 285 continued MTX and 113 had no background DMARDs. Baseline characteristics were similar. At week 16, ACR20 response was achieved by 72/285 (25.3%) of placebo+continued MTX and 14/113 (12.4%) of placebo only patients (nominal p=0.005); for ACR50 these numbers were 25/285 (8.4%) versus 1/113 (0.9%; nominal p=0.003) and for ACR70 they were 8/285 (2.8%) versus 0/113 (0%; nominal p=0.112). Also, more patients with placebo+continued MTX achieved CDAI-LDA at week 16 (25/285; 8.8%) compared with placebo only (2/113; 1.8%; nominal p=0.013). CONCLUSION: Clinical responses to placebo are higher in patients who continue an insufficient MTX background therapy. This suggests an inadvertently more consequent intake of background therapy during the trial. Background therapy should therefore be effectively aligned before enrollment into a clinical trial.