After Tns site--directedmutugenesis, the 2. 6 kb DNA withTn5 insertion lost such complementationability. Therefore, we could concludethat 2. 6 kb DNA fragment containedthe exo gene which complements thethree mutants.

• 6kb片段经Tn5定位突变后丧失这种恢复能力，表明该片段带有对应于3个变种的野生型基因。