Introduction:
The first blotting technique was developed by Ed Southern, and is eponymously known as Southern blotting. In this method fragments of DNA, generated by restriction digestion, are subjected to agarose gel electrophoresis. The separated fragments are then transferred to a nitrocellulose or nylon membrane by a 'blotting' technique. The original method used capillary blotting. Although other methods such as vacuum blotting and electroblotting have been devised, the original method is still used extensively.
Although Southern blotting is a very simple technique, it has many applications, and has been an invaluable method in gene analysis. The same technique can also be used with RNA, as opposed to DNA, and in this case is known as Northern blotting. It is most useful in determining hybridization patterns in mRNA samples, and can be used to determine which regions of a cloned DNA fragment will hybridize to a particular mRNA. However, it is more often used as a method of measuring transcript levels during expression of a particular gene. There are two further variations on the blotting theme. If nucleic acid samples are not subjected to electrophoresis, but are spotted onto the filters, hybridization can be carried out as for Northern and Southern blots. This technique is known as dot-blotting, and is particularly useful in obtaining quantitative data in the study of gene expression. The final technique is known as Western blotting, and this involves the transfer of electrophoretically separated protein molecules to membranes.
