Nonradioactive Probes - Biotin Labelled Proteins - Recent advances In nucleic acid technology now offer alternatives to radioactively labelled probes. One procedure that is becoming increasingly popular is biotin labelling of nucleic acids. This system .exploits the affinity, which the glycoprotein 'avidin' has for biotin (vitamin H). Avidin is commonly found In egg white.

Biotinylated probes are prepared through a nick-, translation reaction by replacing nucleotides with biotinylated derivatives. After hybridization and washing, detection of hybrids is done by a series of cytochemical reactions which finally give a blue colour whose intensity is proportional to the amount of biotin in the hybrid.

There are several advantages of using biotinylated probes. For example, these assays employ non toxic materials, whose half-life is longer. These probes can be prepared in advance in bulk and stored at - 20°C for repeated uses. Detection of hybrids is much faster than by radioactive probes.