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The set of regulatory interactions between genes, mediated by transcription factors (TFs) forms a
complex transcriptional regulatory network (TRN). For the bacterium E. coli we mapped microarray expression
data onto the TRN to study the correspondence between a gene's expression level and its TRN characteristics
at different levels of network organization.
First, we find that pairwise interactions alone between a regulating and a regulated gene are not necessarily reflected in their expression profiles. Second, we observe that the effect of mutations in single genes always spreads globally throughout the TRN but preferentially alters expression levels within the sub-network of downstream genes. Third, we see that absolute gene expression varies with the number of regulated genes: Non-regulatory genes show a large variability compared to genes coding for TFs. Counterintuitively, we find that for mutants in global regulators the amount of control the TRN exerts on the expression levels is significantly increased compared to the wildtype. We discuss, how this finding can be understood from an evolutionary perspective. |
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