Invariant Distribution of Promoter Activities in Escherichia coli

Cells need to allocate their limited resources to express a wide range of genes. To understand how Escherichia coli partitions its transcriptional resources between its different promoters, we employ a robotic assay using a comprehensive reporter strain library for E. coli to measure promoter activity on a genomic scale at high-temporal resolution and accuracy. This allows continuous tracking of promoter activity as cells change their growth rate from exponential to stationary phase in different media. We find a heavy-tailed distribution of promoter activities, with promoter activities spanning several orders of magnitude. While the shape of the distribution is almost completely independent of the growth conditions, the identity of the promoters expressed at different levels does depend on them. Translation machinery genes, however, keep the same relative expression levels in the distribution across conditions, and their fractional promoter activity tracks growth rate tightly. We present a simple optimization model for resource allocation which suggests that the observed invariant distributions might maximize growth rate. These invariant features of the distribution of promoter activities may suggest design constraints that shape the allocation of transcriptional resources

Case-Control Study of Lung Function in World Trade Center Health Registry Area Residents and Workers

Rationale: Residents and area workers who inhaled dust and fumes from the World Trade Center disaster reported lower respiratory symptoms in two World Trade Center Health Registry surveys (2003–2004 and 2006–2007), but lung function data were lacking. Objectives: To examine the relationship between persistent respiratory symptoms and pulmonary function in a nested case–control study of exposed adult residents and area workers 7–8 years after September 11, 2001. Methods: Registrants reporting post September 11th onset of a lower respiratory symptom in the first survey and the same symptom in the second survey were solicited as potential cases. Registrants without lower respiratory symptoms in either Registry survey were solicited as potential control subjects. Final case–control status was determined by lower respiratory symptoms at a third interview (the study), when spirometry and impulse oscillometry were also performed. Measurements and Main Results: We identified 180 cases and 473 control subjects. Cases were more likely than control subjects to have abnormal spirometry (19% vs. 11%; P,0.05), and impulse oscillometry measurements of elevated airway resistance (R5; 68% vs. 27%; P,0.0001) and frequency dependence of resistance (R5–20; 36% vs. 7%; P , 0.0001). When spirometry was normal, cases were more likely than control subjects to have elevated R5 and R5–20 (62% vs. 25% and 27% vs. 6%, respectively; both P , 0.0001). Associations between symptoms and oscillometry held when factors significant in bivariate comparisons (body mass index, spirometry, and exposures) were analyzed using logistic regression. Conclusions: This study links persistent respiratory symptoms and oscillometric abnormalities in World Trade Center–exposed residents and area workers. ElevatedR5andR5–20 in cases despite normal spirometry suggested distal airway dysfunction as a mechanism for symptoms

Recognition of aminoacyl-tRNA: a common molecular mechanism revealed by cryo-EM

The accuracy of ribosomal translation is achieved by an initial selection and a proofreading step, mediated by EF-Tu, which forms a ternary complex with aminoacyl(aa)-tRNA. To study the binding modes of different aa-tRNAs, we compared cryo-EM maps of the kirromycin-stalled ribosome bound with ternary complexes containing Phe-tRNAPhe, Trp-tRNATrp, or Leu-tRNALeuI. The three maps suggest a common binding manner of cognate aa-tRNAs in their specific binding with both the ribosome and EF-Tu. All three aa-tRNAs have the same ‘loaded spring' conformation with a kink and twist between the D-stem and anticodon stem. The three complexes are similarly integrated in an interaction network, extending from the anticodon loop through h44 and protein S12 to the EF-Tu-binding CCA end of aa-tRNA, proposed to signal cognate codon–anticodon interaction to the GTPase centre and tune the accuracy of aa-tRNA selection

Resonant photoemission at the 2p edge in compounds containing Mn with different valences

We have investigated the Raman-Auger crossover of the Mn 2p non-radiative decays in bulk MnO. For the highest kinetic energy transition in the Mn 2p3p3p decay, Raman behaviour is observed up to approximate to 3.4 eV above the resonance energy (maximum of the L-3 absorption). In the case of the 2p3p3d and 2p3d3d transitions a similar situation occurs up to approximate to 5 eV above the resonance energy. We compare these results to those obtained on a thin MnO layer deposited on Cu, on bulk Mn and on La0.7Sr0.3MnO3. The results are discussed in terms of the screening dynamics of the Mn 2p core hole and of the metallic/insulating character of the material. (c) 2005 Elsevier B.V. All rights reserved