Abstract: The instant invention provides a means for quantitatively determining the vel of tumor suppressor gene p53 by determination of level of messenger ribonucleic acid (mRNA) of the gene in a sample when compared with a prepared standard. The assay is quantitative in that the specific number of copies of the p53 mRNA in a sample may be derived from a curve from a standard of p53 RNA. The RNA used in preparation of a standard curve to quantitate RNA is generated using a plasmid which is part of the invention. In the assay, the RNA is produced by a protein (RNA polymerase) that reads the DNA message and manufactures an RNA copy. The RNA content of the transcribed sample is determined spectrophotometrically to measure the molar concentration.