Expansion
SNoW DRoP: Southern DNA, Northern RNA, Western Protein
Expansion
SNoW DRoP, reading the two lines against each other:
- Southern - DNA
- Northern - RNA
- Western - Protein
“Southern is the only one named after a person”, Edwin Southern, and the others were named jokingly by analogy, which is why the compass directions have no meaning.
Method, common to all three:
- Separate by size using gel electrophoresis
- Transfer (blot) onto a membrane
- Probe: a labelled complementary nucleic acid for Southern and Northern, a labelled antibody for Western
- Visualise
Uses
- Southern: gene structure, restriction fragment length polymorphisms, repeat expansions such as fragile X and Huntington’s
- Northern: gene expression, measuring mRNA levels
- Western: protein presence and size. Used to confirm HIV historically, and for prion disease and specific protein deficiencies
Related techniques: Southwestern blotting detects DNA binding proteins, and ELISA detects protein in solution rather than after electrophoresis, so it quantifies but does not give size.