Polyribosomes and unstable messenger RNA. II. Some further implications of the Tape theory of protein synthesis

Abstract

An analysis of sedimentation profile of rapidly labelled RNA and distribution of nascent peptides on polyribosomes has been carried out on the basis of a model of protein synthesis described in an earlier paper. It is concluded that the observed sedimentation profile of rapidly labelled RNA in bacteria does not necessarily represent the size distribution of intact messenger RNA's. The characteristic "8 to 12 s" peak often referred to in literature is shown to be a function of translational rate, half-life of messenger RNA and duration of pulse-labelling. The model further predicts that the position of this peak should shift towards larger s values with an increase in labelling period until it approaches a steadystate value determined by translational rate and half-life of messenger RNA. Kinetic curves derived from these analyses closely resemble the observed labelling pattern. Complex distribution pattern for nascent peptides on polyribosomes in bacteria inferred from amino acid incorporation profile is attributed to instability and polycistronic nature of messenger RNA's.