Dot, Southern, and Northern Blots

Abstract

Nucleic acid hybridization on solid supports (nitrocellulose or nylon membranes) has become one of the most important techniques in molecular biology. Here, we will specifically deal with applications of the digoxigenin (DIG) system in dot blot, Southern, and northern blot hybridizations. In principle molecular hybridization is the formation of double-stranded nucleic acid molecules by sequence-specific base pairing of complementary single strands. For dot blot hybridization, DNA or RNA is spotted directly onto a membrane, while for Southern or northern blot hybridization DNA fragments or mRNAs, respectively, are transferred to the membrane after size separation on an agarose gel by capillary-, vacuum-, pressure-or electroblotting and subsequently hybridized with a labeled probe that can detect a specific sequence. How to prepare DNA or RNA agarose gels is described elsewhere (see Sambrook et al., 1989).