The kinetics of the translation of messenger RNA into protein

Descriptions of incorporation of radioactively labeled amino acid into polyribosomes and polypeptide have been developed. Each treatment considers a population of cells active in protein synthesis which is suddenly exposed to a labeled amino acid and assumes that the cells possess concentrations of stable mRNA, of ribosomes, and of tRNA, that remain constant with time. By assuming further that each ribosome spends a fixed interval at each codon and that the amount of label available as amino acyl-tRNA is a step function, simple equations are obtained. These equations will probably prove to be mostly of heuristic value in evaluating experimental data. An alternative treatment which has more promise as a means of fitting experimental data is developed by assuming that there is an exponential decline in the number of ribosomes initially occupying a given codon and that the amount of label in amino acyl tRNA approaches a constant value exponentially. The theories indicate how kinetic data for labeling of polyribosomes and polypeptides can be used to locate slowdowns in mRNA translation.