Ribosome shut-down by 16S rRNA fragmentation in stationary phase E. coli

Stationary-phase bacterial cells are characterized by vastly reduced metabolic activities yielding a dormant-like phenotype. Several hibernation programs ensure the establishment and maintenance of this resting growth state. Some of the stationary phase-specific modulations affect the ribosome and its translational activity directly. In stationary-phase Escherichia coli, we observed the appearance of a 16S rRNA fragmentation event at the tip of helix 6 within the small ribosomal subunit (30S). Stationary-phase 30S subunits showed markedly reduced activities in protein biosynthesis. On the other hand, the functional performance of stationary-phase large ribosomal subunits (50S) was indistinguishable from particles isolated from exponentially growing cells. Introduction of the 16S rRNA cut in vitro at helix 6 of exponential phase 30S subunits renders them less efficient in protein biosynthesis. This indicates that the helix 6 fragmentation is necessary and sufficient to attenuate translational activities of 30S ribosomal subunits. These results suggest that stationary phase specific cleavage of 16S rRNA within the 30S subunit is an efficient means to reduce global translation activities under non-proliferating growth conditions. To understand better the process of before-mentioned 16S rRNA fragmentation and its physiological importance we are currently in the process of identifying factors involved. In addition, by mutating sequence of the helix 6 we want to identify important structural properties of the helix and the role of the before-mentioned 16S rRNA fragmentation in the cellular physiology. In addition, we have indications that similar fragmentation is present in distinctly related bacterial species