Distribution of the three categories of genes (GCO, nGCO and genes with no homolog in E. coli ) in the complete Salmonella gene set and in the subsets of HNS repressed genes and essential genes . GCO genes are overrepresented in the essential gene set and underrepresented in HNS repressed genes. In contrary, nGCO genes and genes with no homolog in E. coli are overrepresented in HNS repressed genes. As expected, we observed that genes with no homolog in E. coli are underrepresented in the essential gene set. In the random dataset we observe the same representation as in the overall Salmonella genome. The same coloring scheme with Fig. 1B. is used for easy comparison.