A number of methods are available for assessing messenger ribonucleic acid (mRNA) levels, namely, reverse-transcription polymerase chain reaction (RT-PCR), Northern blot analysis, primer extension, and RNA protection assays (1 ). Because of the PCR amplification step, RT-PCR has the important advantage that little RNA is required. In addition, RT-PCR is a relatively simple procedure that does not have an absolute requirement for the use of radioisotopes. Northern blot analysis requires at least ten times as much sample, radioisotopes, and the results obtained are, at best, semiquantitative. Northern blot analysis also is technically more difficult since electrophoresis of mRNA, a blotting step, and autoradiography are required.
