The hybrid signals are then detected by X-ray film and can be quantified by densitometry. The membrane is washed to ensure that the probe has bound specifically and to prevent background signals from arising. Experimental conditions that can affect the efficiency and specificity of hybridization include ionic strength, viscosity, duplex length, mismatched base pairs, and base composition. After a probe has been labeled, it is hybridized to the RNA on the membrane. Once the RNA has been transferred to the membrane, it is immobilized through covalent linkage to the membrane by UV light or heat. The transfer buffer used for the blotting usually contains formamide because it lowers the annealing temperature of the probe-RNA interaction, thus eliminating the need for high temperatures, which could cause RNA degradation. Ĭapillary blotting system setup for the transfer of RNA from an electrophoresis gel to a blotting membrane.Ī nylon membrane with a positive charge is the most effective for use in northern blotting since the negatively charged nucleic acids have a high affinity for them. The major difference is that RNA, rather than DNA, is analyzed in the northern blot. Northern blotting takes its name from its similarity to the first blotting technique, the Southern blot, named for biologist Edwin Southern. The northern blot technique was developed in 1977 by James Alwine, David Kemp, and George Stark at Stanford University. However, the entire process is commonly referred to as northern blotting. Strictly speaking, the term 'northern blot' refers specifically to the capillary transfer of RNA from the electrophoresis gel to the blotting membrane. Northern blotting involves the use of electrophoresis to separate RNA samples by size, and detection with a hybridization probe complementary to part of or the entire target sequence. With northern blotting it is possible to observe cellular control over structure and function by determining the particular gene expression rates during differentiation and morphogenesis, as well as in abnormal or diseased conditions. The northern blot, or RNA blot, is a technique used in molecular biology research to study gene expression by detection of RNA (or isolated mRNA) in a sample.
Flow diagram outlining the general procedure for RNA detection by northern blotting.
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