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After the separation of protein or nucleic acids by electrophoresis, the molecule of interest is blotted onto a membrane. Specific RNA or DNA fragments are identified by hybridization with probes consisting of labeled DNA (Southern blotting) or RNA (Northern blotting) sequences. Labeled antibodies are used to probe for specific proteins in Western blotting, and fluorescence-based detection enables multiplex detection of several proteins simultaneously. Similar approaches can be applied to identify post-translational modifications of proteins (Eastern blotting), non-antibody protein-protein interactions (Far-Western blotting), protein-DNA interactions (Southwestern blotting), and protein-RNA interactions (Northwestern blotting).
There are other nucleic acid blotting methods, such as dot blots, slot blots, and colony/plaque lifts that do not include electrophoresis. Dot and slot blots involve direct application of the sample to the membrane, which is then probed. Colony and plaque lifts involve direct transfer of colonies of microorganisms from a culture plate onto a membrane which is probed.