The Ribosomal Components Involved in EF-G- and EF-Tu-dependent GTP Hydrolysis

Abstract

INTRODUCTION
This review concerns recent developments in the determination of the ribosomal components involved in GTP hydrolysis, which is dependent on the peptide chain elongation factors Tu (EF-Tu) and G (EF-G).

EF-Tu participates with GTP in the enzymatic binding of aminoacyl-tRNA to the ribosomal A site, whereas EF-G is necessary for translocation of peptidyl-tRNA from the A site to the P site, messenger movement, and ejection of “spent” tRNA. There is general agreement that EF-G and EF-Tu bind to a common region on the ribosome and that this region promotes the cleavage of GTP. Convincing evidence has been accumulated that two ribosomal proteins of the large ribosomal subunit play an equally important part in the transient attachment of the elongation factors EF-G and EF-Tu to the ribosome and thus in the induction of GTPase activity. The two proteins, known as L7 and L12, have structural properties that are unique among the ribosomal proteins and are also identical proteins except for the presence of an acetyl group on the N-terminal serine of L12.

The L7 and L12 requirement for GTP hydrolysis in a number of partial reactions in protein synthesis are described here, and examples are given to support proximity of the peptidyl transferase center and the GTPase center in terms of common ribosomal components. This proximity raises the question of how the ribosome controls the proper temporal succession by which EF-Tu and EF-G exert their function in tRNA binding and translocation. The functional state of the ribosome, as determined by...