S1 nuclease is an endonuclease that is active against single-stranded DNA and RNA molecules. It is five times more active on DNA than RNA. Although its primary substrate is single-stranded, it can also occasionally introduce single-stranded breaks in double-stranded DNA or RNA, or DNA-RNA hybrids. S1 nuclease is used in the laboratory as a reagent in nuclease protection assays. In molecular biology, it is used in removing single stranded tails from DNA molecules to create blunt ended molecules and opening hairpin loops generated during synthesis of double stranded cDNA.
