Figure 1.

Southern blot analysis of revertants mimp1/impala. Genomic DNA of co‐transformant M7 and derived revertants was digested by XbaI and membranes were successively probed with: (A) a 419‐bp‐long niaD probe obtained by polymerase chain reaction (PCR) on the pAN301 plasmid using primers niaCG1 and niaCG2; and (B) a 120‐bp‐long mimp1‐specific probe amplified from the pNm1H18 plasmid using the primers mi1 and SacF. The revertants showed a single niaD band of 1.7 kb, i.e. 224 bp shorter than the corresponding band of the co‐transformant (approximately 1.9 kb), thereby demonstrating the excision of mimp1 from the nitrate reductase gene (A). The asterisks indicate reinsertion events of the mimp1 element. In lane 5 (black rectangle), the excision of mimp1 was not followed by a reinsertion event (B).