Motifs in gene transcription regulatory networks

A brief overview is given of the structure and evolution of gene transcription regulatory networks (GTRNs) of simple organisms like Escherichia coli and yeast Saccharomyces cerevisiae. A prominent motif appearing in the GTRNs is the feed forward loop (FFL). The FFLs have essential functions in gene regulatory processes and it is desirable that the operational noise of a FFL be kept at the minimum for reliability of signal transmission. We calculate the variances around the mean protein levels in the steady states of Type-1 and Type-4 coherent FFLs using a stochastic model of gene expression and the Langevin formalism. The Type-1 FFL is found to be less noisy than the Type-4 FFL. Type-1 FFL motif is more abundant than Type-4 FFL motif in GTRNs. This leads to the conjecture that noise is one of the evolvable traits on which natural selection acts.