A rapid method of non radioactive Northern blot analysis.

The electrophoretic determination of RNA size by Northern blot analysis is an important procedure that has required to date the use of radiolabelled cDNA and cRNA probes. Here, we describe a new method which allows the size of an mRNA to be visualized by use of oligonucleotide probes directly labelled with alkaline phosphatase (AP). One advantage compared to radiolabelled probes is that AP-labelled oligonucleotides are stable at 4°C for up to 4 years without any loss of enzyme activity. In addition, once a membrane has been hybridized with the AP-labelled oligonucleotide, an mRNA signal may be obtained within 4 hrs following stringent washing of the membrane. Existing procedures that employ radiolabelled cDNA and cRNA probes require prolonged exposure of the membrane to autoradiography film to obtain a signal, especially if the radioisotope S is used. This exposure time may be shortened somewhat if P is used to label the probe. However, many laboratories avoid the use of P because of the health and contamination risks involved and the short half-life of the isotope. The use of enzyme-labelled oligonucleotides for Northern blot analysis overcomes these problems.