Ribosome Modulation Factor

Abstract

Ribosome modulation factor (RMF) is a ribosome-associated protein in Escherichia coli that is synthesised under stringent control during stationary phase and during periods of slow growth. The binding of RMF seems to make ribosomes, and in particular ribosomal RNA (rRNA), more resistant to degradation. Comparison of RMF-deficient mutant strains and the parent strain suggest that RMF contributes to the survival of E. coli under environmental extremes, such as conditions of heat, cold, acid, and osmotic stress. RMF may bind to inactive ribosomes to produce a stable resting state. Because binding blocks the peptidyl transferase site, ribosomes with associated RMF are not capable of protein synthesis. It has, therefore, been further suggested that RMF binding serves to inactivate excess ribosomes to make protein synthesis more efficient under conditions of slow growth. RMF binding is associated with the formation of 100 S ribosome dimers that are observed after sucrose density centrifugation of extracts of stationary-phase cultures. Dimer for- mation is generally seen as an inherent feature of RMF function, but evidence that this may not be the case is discussed in this review. The exact function and mecha- nism of action of RMF, therefore, remain to be fully elucidated.