Measurement of NOS mRNA by Northern Blotting and the Ribonuclease-Protection Assay

The amount of RNA varies greatly between different cell types and organisms, and the majority of RNA (more than 95%) consists of ribosomal RNA (28S, 18S, and 5S species) and the tRNA. Only a small proportion (usually less than 1% of the total amount) of RNA corresponds to the mRNA species. However, in order to improve mRNA-detection methods, preparations of enriched-mRNA content (poly-A⁺ ) can be obtained after elution from oligo-dT columns of total-RNA samples.