In fact, most bacterial proteins are synthesized within the unit of operons, i.e. all the proteins in an operon are linked. They are not independent and are synthesized together. So the x in the formula should be the number of the addition of all operons and independent proteins in the genome. For example, the number of operons in E. coli is 834 [10] , with the number of independent proteins, together amounts to about 2,584. The x should be 2,584 for E. coli. Because the number of operons in most bacteria genomes is still unavailable at the present time, we calculated I 2 based on the number of proteins.