ANALYSIS OF THE INTERACTION BETWEEN BOVINE MITOCHONDRIAL 28-S RIBOSOMAL-SUBUNITS AND MESSENGER-RNA

The small subunit of the bovine mitochondrial ribosome forms a tight c omplex with mRNAs. This [28 S:mRNA] complex forms as readily on circul ar mRNAs as on linear mRNAs indicating that a free 5' end on the mRNA is not required fut the interaction observed. The effects of monovalen t cations on the equilibrium association constant and on the forward a nd reverse rare constants governing this interaction have been determi ned, Monovalent cations have a strong effect on the ii,I-ward rate con stant. Increasing tile KCl concentration from 1 mM to 100 mM reduces k (off) by nearly 100-fold. Monovalent cations have only a small effect on the reverse rate constant, k(on). Analysis of these data indicates that the rate laws governing the Formation and dissociation of the [28 S:mRNA] complex cannot be deduced from the chemical equation. This ob servation suggests that there are 'hidden intermediates' in the format ion and dissociation of this complex. The implications of these observ ations are discussed in terms of a model for the interaction between t he mitochondrial 28 S subunit and mRNAs.