Recognition of sequence-directed structure of the ssDNA backbone by nucleases

Escherichia coli endonuclease I and exonuclease VII appear to recognize sequence-dependent conformations in the ssDNA backbone. ssDNAs, containing either A- and/or T-tract or a CAP binding region, were digested with these nucleases under conditions which minimize the formation of secondary structures. The digestion patterns were examined in relation to previous results of biochemical and crystallographic studies on dsDNA, and showed broad agreement. Endonuclease I cleaved ssDNA at sites corresponding to bent sites in dsDNA.