Enzyme that produces single strand nicks in DNA:

Deoxyribonuclease I (DNAase I) Acts on single-stranded DNA, double-stranded DNA, and chromatin. Makes single stranded cuts in nearly any segment of DNA i.e. has low sequence specificity. Digest DNA that is not protected/not bound by protein, into its component deoxynucleotides. Used in DNA Foot Printing. E.g. (DNase I) nick the single strands of double-stranded DNA.