, 2007). The evolutionary reasons that maintain this structure have remained unknown given that TRNs are poorly conserved across bacterial species and global regulators do not necessarily share similar evolutionary STI571 cost histories nor necessarily regulate similar metabolic responses in different organisms (Lozada-Chvez et al., 2006). Here, we analyze this issue through different genomic and bioinformatics approaches using experimental and compiled data of TFs and their bsDNAs from Escherichia coli and Bacillus subtilis, the two best known prokaryotic TRNs with click here remarkably different

niches and evolutionary histories (Lozada-Chvez et al., 2006). We found that paralogy relationships are insufficient to explain the global or local role observed for TFs within regulatory networks, as previously reported (Consentino et al., 2007). Our results provide a picture in which DNA-binding specificity, a molecular property defined here as the ability of DNA-binding proteins (TFs) to discriminate a small subset of DNA sequences from the vast

repertoire of sequences found in a genome, is a predictor of the role of TFs. In particular, we observed that global regulators consistently display low levels of binding specificity, while displaying comparatively higher expression values in microarray experiments. In addition, we found a strong negative correlation between binding specificity and the number of co-regulators that help to coordinate genetic expression BKM120 on a genomic scale. A close look at several orthologous TFs, including FNR, a regulator found to be global in E. coli and local in B. subtilis,

confirms the diagnostic value of specificity in order to understand their regulatory function, and highlights the importance of evaluating the metabolic and ecological relevance of effectors as another variable in the evolutionary equation of regulatory networks. Finally, a general model that integrates some evolutionary forces and molecular properties is presented, aiming to explain Protein Tyrosine Kinase inhibitor how regulatory modules (regulons) grow and shrink, as bacteria have tuned their regulation to increase adaptation from their Early Evolution to the current Life. Cosentino Lagomarsino, M., Jona, P., Bassetti, B. and Isambert, H. (2007). Hierarchy and feedback in the evolution of the Escherichia coli transcription network. Proceedings of the National Academy of Sciences USA, 104: 5516–5520. Lozada-Chavez, I., Janga, S. C. and Collado-Vides, J. (2006). Bacterial regulatory networks are extremely flexible in evolution. Nucleic Acids Research, 34: 3434–3445. E-mail: ilozada@ccg.​unam.​mx Theoretical Study of the Adsorption of RNA Bases on a Surface of Na + -Montmorillonite Pierre Mignon1, Piero Ugliengo2, Mariona Sodupe1 1 Universitat Autònoma de Barcelona, Dep. Quimica, 08193 Bellaterra, Spain; 2University of Torino, Dip. Chimica IFM, Via P. Giuria, 7.