Figure 2.

Age distribution of horizontally transferred DNA in the E. coli MG1655 chromosome. Bars represent the amount of protein-coding, horizontally transferred DNA of the specified age present in the 571 genes analyzed by back amelioration. The remaining 184 genes could not be successfully analyzed because of aberrant nucleotide compositions, which could result from horizontal transfer among more than one genome; most of the genes comprising this group are encoded by prophages and mobile genetic elements.