Z-DNA-forming sequences are spontaneous deletion hot spots.

Z-DNA-forming sequences are shown to elicit a biological response in Escherichia coli. Plasmids containing sequences capable of adopting the Z conformation (GC and CA/GT) are shown to be hot spots for spontaneous deletions. All the deletions involve an even number of base pairs. The distribution of the deletion events shows that the process ends when the Z-DNA-forming sequence has been reduced to a size no longer capable of adopting the Z conformation at natural superhelical density.