S1+nuclease+protection

=S1 nuclease protection=

**S1 nuclease protection** is a method used in transcript analysis to ascertain the start site of transcription.

The procedure is as follows:

**1.** Design a 5' end-labelled probe to hybridise to a region on DNA spanning the transcription start point - i.e. from within the promoter to within exon 1. **2.** Hybridise this probe to the transcript. **3.** Digest with S1 nuclease; the hybridised region is protected and the rest is degraded **4.** An unknown number of nucleotides (x nts) has been removed from the 3' end of the probe; ascertain x using electrophoresis with 3 lanes:

- Markers - Probe - Protected probe

**5.** The distance on the gel between the probe and the protected probe corresponds to x nts.