HucO is regulated by HucR. When uric acid is abscent, HucR can bind to hucO making downstream gene silencing. Lysis1 and Lysis2 are lyases. Lysis1siRNA286 can inhibit Lysis1, and Lysis2siRNA106 can inhibit Lysis2. When both plasmids are simultaneously expressed, the lyases are inhibited. But if any plasmid is lost or HucR combined hucO，part3 will not be expressed. And the bacterium is cleaved by the Lysis2 . A series of things happens when bacteria are excreted: First, the concentration of uric acid get lower. Second, the hucO of part3 is suppressed by HucR and cannot work. Next, Lysis2 siRNA106 cannot inhibit Lysis2. Finally, the bacteria are cleaved by Lysis2. To test the lethal ability of part2 and part3, and the regulation of uric acid on part3 we did four sets of experiments.