Difference Between Functional and Structural Integrity of Messenger RNA

Messenger RNA molecules that are structurally stable, as measured by their ability to hybridize to DNA, may nevertheless be considerably less stable in retaining their ability to function in protein synthesis. The structure of the majority of the mRNA of phage S13 decays with a half-life of 10.6 +/- 0.5 min. In contrast, much of the function of the mRNA that is involved in synthesis of a capsid protein (product of the F gene) decays rapidly with a half-life of 1.4 +/- 0.8 min; a residual amount of function decays with a half-life of 14.0 +/- 4.0 min. The measurements were made in the presence of rifampicin, which was used to prevent the formation of new mRNA. A proposed model for the functional decay is based on the polycistronic nature of the mRNA. Degradation of the mRNA would proceed in two steps: the first step would be a fast attack at a region near the 5'-terminus of each molecule that would eliminate the function of the proximal message; the second step would be a slow attack on the remaining messenger molecule precipitating a subsequent rapid degradation of the physical structure.