S1 Protection

**Semantic type:** Laboratory Procedure

**Definition:** Molecular biology procedure used to determine the 5' end or 3' end of a nucleic acid molecule, or the location of the junction between spliced molecules. Used most commonly to determine the 5' end of RNA transcripts. Based on the protection afforded an end-labeled DNA probe from nuclease S1 digestion after hybridization with a target molecule. The length of the protected probe indicates the end or molecular junction of the target nucleic acid sequence.