Researchers interested in gene expression have at their disposal a whole host of RNA profiling tools, including Northern blotting, microarray analysis, and RNase protection assays (RPA). Each of these techniques has advantages and disadvantages, and scientists must decide which approach will best suit their particular need. A Northern blotting experiment involves the electrophoretic resolution of RNA samples on a formaldehyde-agarose gel, transfer of the RNA onto a solid support (such as a nitrocellulose or nylon membrane), and the detection of specific transcripts using a labeled probe. RNA samples may be either total RNA (unpurified) or poly-A+ RNA (purified mRNA). Because mRNA represents only a small fraction of the total cellular RNA, Northern blots using total RNA samples require considerably more RNA than do those using poly-A+ RNA.

One advantage of Northern blotting is the ease with which comparative analyses can be carried out, as researchers can run...

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