S1 Nuclease preferentially degrades single-stranded nucleic acids, such as DNA-DNA, DNA-RNA, and RNA-RNA, to yield 5’-phosphoryl mono- or oligo-nucleotides. It has a slight preference for DNA over RNA. S1 Nuclease is used for removal of single-strand overhangs in duplex DNA, selective degradation of single-stranded DNA or RNA, and transcript mapping.