Biotin-modified nucleic acid, hybridization

Chemically modified DNAs can also be used as hybridization probes, provided that the modification does not interfere with the formation of hybrid DNA molecules. A psoralen biotin label has also been developed. Psoralen is a photoactivable agent that can intercalates into single- or double-stranded nucleic acids. On irradiation at 365 nm, it will covalently bind to the probes. This labeling reaction is simple and straightforward. However, the reagents for labeling and detection are only available in a kit format. 

Probes prepared with either digoxigenin- or biotin-modified nucleotides can be hybridized to Southern blots to detect target nucleic acid sequences. These methods offer an attractive alternative to radioactively tagged probes in terms of safety, cost, and efficiency. Most previous nonradioactive strategies utilized the detection of the modified base by the use of a coupled antibody- or avidin-alkaline phosphatase. The blot with the bound alkaline phosphatase was then treated with a compound, such as Nitro Blue Tetrazolium (NBT), that was converted to an insoluble, colored compound at the site of hybridization, thus facilitating visualization of the hybridized probe. 

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