Action of Single-strand-specific S1 Endonuclease on Locally Altered Structures in Double-stranded DNA

Abstract

The cleavage of double-stranded DNA by S1 endonuclease was studied by sucrose density gradient centrifugation analysis. The enzyme introduced no single-strand breaks into native T 7 DNA under conditions where heat-denatured T 7 DNA was completely degraded. By using enzyme at about 6 times higher the amount required for complete degradation of the heat-denatured DNA, it was possible to make a few single-strand breaks in native T 7 DNA. Under the conditions where native T 7 DNA is absolutely resistant to the enzyme, the susceptibility of locally altered structures naturally present and/or artificially induced in native double-stranded DNA to the enzyme was studied. It was evidenced that S1 endonuclease can cleave circular covalently closed, superhelical fl RFI DNA, depurinated T 7 DNA, bleomycin-treated T 7 DNA containing internal single-strand breaks, but not cleave intercalating drug-bound T 7 DNA.