We applied the FTF methodology to E. coli using expression datasets obtained from the NIH omnibus service: GSE7 (physiological and genetic changes that affect tryptophan metabolism), GSE8 (chromosomal replication forks in synchronized cells) and GSE9 (UV exposure). These 65 sets were chosen as the experiments were performed on the same platform. One single run of FTF on a PC (Xeon 2.4 GHz) takes about 15 minutes and requires 700 MB memory. The probability distributions for the absolute value of the Pearson correlation coefficient between the constructed TF activities (using equation 2) and expression data are shown in Fig. 6 for both the training and random sets. A comparison of Fig. 6 and Fig. 1 shows that by constructing TF activities using a preliminary TRN, we significantly increase the amount of information extracted from expression data.