Northern Analysis and Nucleic Acid Probes

Soon after the introduction of the Southern blotting procedure (1 ), an analogous technique, known as northern blotting, was developed for the analysis of RNA sequences (2 ). Both procedures rely on the annealing (hybridization) of complementary single-stranded nucleic acid molecules under suitable conditions (3 ). Nucleic acids separated by size using agarose gel electrophoresis are transferred onto a solid support (membrane) and hybridized to complementary radiolabeled nucleic acid sequences. Whereas in Southern blotting experiments, DNA is transferred from a gel to a membrane and hybridized (see Chapter 13 , this volume), in northern blotting it is RNA that is fractionated, immobilized on a membrane, and hybridized to a probe.