Interaction of Eukaryotic Ribosomes with Messenger RNA: Evidence for a Scanning Mechanism

Abstract

The question of how ribosomes select the correct AUG codon for initiation of protein synthesis is intriguing. In prokaryotes, both the primary and secondary structure of the mRNA contribute to the specificity of initiation: a purine-rich sequence located ~ 10 nucleotides upstream of the AUG (or GUG) codon serves as a positive recognition element for binding of E. coli ribosomes (Steitz and Jakes 1975), while the secondary and tertiary structure of the message play an important negative role (Lodish 1970). Thus, denaturation of coliphage f2 RNA (with or without cleavage of the RNA backbone) dramatically increased binding of E. coli ribosomes to the synthetase and A-protein cistrons, and also allowed initiation at a few spurious sites. Perturbation of mRNA structure also alters the specificity of initiation by eukaryotic ribosomes, but the effects are quite different from those observed in prokaryotic systems.