Concerning the kinetics of polypeptide synthesis on polyribosomes

Abstract

The kinetics of biosynthesis of polypeptides on polyribosomes is analyzed in accordance with a simple mathematical model. Each ribosome is assumed to block L adjacent. (m‐RNA) template sites but to move a distance of one, and only one, template site (nucleotide triplet) upon the addition of each monomer unit to the growing polypeptide chain bound to it. Solutions are sought, for the probability, n j(t), that a template possesses, at time t, a polypeptide chain that has reached degree of polymerization j. Several classes of steady‐state solutions are obtained via machine computation. These correspond to various choices of relative rates of initiation, polymerization along templates, and termination (release of completed chains from templates). Experimental data available from radioactive pulse labeling experiments are discussed. The data obtained by Dintzis, and by Winslow and Ingram, in studies of the synthesis of the α chain of rabbit hemoglobin and human hemoglobin, respectively, are consistent with steady‐state solutions obtained from the current theoretical calculations when the rates of initiation and termination are of comparable magnitude and rate‐determining. In this case, a (relatively) small number of chains are polymerized at a (relatively) fast rate each near the beginning of the template, and there exists a transition to a situation near the end of the template in which a (relatively) large number of chains are polymerized at a (relatively) slow rate each. For this solution the situation near the end of the template is entirely analogous to a traffic jam in automobile traffic.