The northern blot is a technique used in molecular biology research to study gene expression. It takes its name from the similarity of the procedure to the Southern blot procedure, named for biologist Edwin Southern, used to study DNA, with the key difference that, in the northern blot, RNA, rather than DNA, is the substance being analyzed by electrophoresis and detection with a hybridization probe. This technique was developed in 1977 by James Alwine, David Kemp, and George Stark at Stanford University.^[1] Molecular biology is the study of biology at a molecular level. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... A Southern blot is a method routinely used in molecular biology to check for the presence of a DNA sequence in a DNA sample. ... Sir Edwin Southern (born 1938) is a 2005 Lasker Award-winning molecular biologist. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... For other uses, see RNA (disambiguation). ... For specific types of electrophoresis (for example, the process of administering medicine, iontophoresis), see electrophoresis (disambiguation). ... A hybridization probe is a short piece of DNA (on the order of 100-500 bases) that is denatured (by heating) into single strands and then radioactively labeled, usually with phosphorus (32P or 33P). ...

The gels may be run on either agarose or denaturing polyacrylamide gels depending on the size of the RNA to be detected. A notable difference in the procedure in case of agarose gels, (as compared with the Southern blot) is the addition of formaldehyde which acts as a denaturant. For smaller fragments denaturing polyacrylamide urea gels are employed. An agarose is a polysaccharide polymer material, generally extracted from seaweed. ... Polyacrylamide is an acrylate polymer formed from acrylamide subunits that is readily cross-linked. ... Formaldehyde is the chemical compound with the formula H2CO. It is the simplest aldehyde-- an organic compound containing a terminal carbonyl group: it consists of exactly one carbonyl. ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known by the International Nonproprietary Name (rINN) carbamide, as established by the World Health Organization. ...

As in the Southern blot, the hybridization probe may be made from DNA or RNA.

A variant of the procedure known as the reverse northern blot is occasionally used. In this procedure, the substrate nucleic acid (that is affixed to the membrane) is a collection of isolated DNA fragments, and the probe is RNA extracted from a tissue and radioactively labelled.

The use of DNA microarrays that have come into widespread use in the late 1990s and early 2000s is more akin to the reverse procedure, in that they involve the use of isolated DNA fragments affixed to a substrate, and hybridization with a probe made from cellular RNA. Thus the reverse procedure, though originally uncommon, enabled the one-at-a-time study of gene expression using northern analysis to evolve into gene expression profiling, in which many (possibly all) of the genes in an organism may have their expression monitored. Example of an approximately 40,000 probe spotted oligo microarray with enlarged inset to show detail. ... Expression Profiling Microarray technology is often used for expression profiling. ...

References

1. ^ Alwine JC, Kemp DJ, Stark GR (1977). "Method for detection of specific RNAs in agarose gels by transfer to diazobenzyloxymethyl-paper and hybridization with DNA probes". Proc. Natl. Acad. Sci. U.S.A. 74 (12): 5350-4. doi:10.1073/pnas.74.12.5350. PMID 414220. 

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

See also

• Southern Blot
• Western Blot
• Far-Eastern blot

A Southern blot is a method routinely used in molecular biology to check for the presence of a DNA sequence in a DNA sample. ... A Western blot. ...

External links

• Northern Blot analysis of mRNA from mammalian polyribosomes (a protocol)
• Northern Blot A great northern blot resource complete with diagram and protocol.