Gene counts of original and reduced GRNs.

The full genomes for E. coli and B. subtilis contain 4,690 genes (according to RegulonDB [12]) and 6121 genes(obtained from SubtiWiki [45]), respectively. Among all genes only 1843 and 2482, respectively, express TFs with known interactions. The first reduction step in E. coli was performed by a trivial fibration (collapsing the operons, which are trivial fibers), before applying CoReSym. This could also be seen as a part of Step 1 and as such is not needed for B. subtilis.