Hibernation as a Stage of Ribosome Functioning
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REVIEW
Hibernation as a Stage of Ribosome Functioning K. S. Usachev1, M. M. Yusupov1,2*, and Sh. Z. Validov1 1
2
Kazan Federal University, 420008 Kazan, Russia Institute of Genetics and Molecular and Cellular Biology, 67400 IllkirchGraffenstaden, France a email: [email protected] Received July 30, 2020 Revised August 28, 2020 Accepted August 28, 2020
Abstract—In response to stress, eubacteria reduce the level of protein synthesis and either disassemble ribosomes into the 30S and 50S subunits or turn them into translationally inactive 70S and 100S complexes. This helps the cell to solve two principal tasks: (i) to reduce the cost of protein biosynthesis under unfavorable conditions, and (ii) to preserve functional ribosomes for rapid recovery of protein synthesis until favorable conditions are restored. All known genes for ribosome silencing factors and hibernation proteins are located in the operons associated with the response to starvation as one of the stress factors, which helps the cells to coordinate the slowdown of protein synthesis with the overall stress response. It is pos sible that hibernation systems work as regulators that coordinate the intensity of protein synthesis with the energy state of bacterial cell. Taking into account the limited amount of nutrients in natural conditions and constant pressure of other stress factors, bacterial ribosome should remain most of time in a complex with the silencing/hibernation proteins. Therefore, hibernation is an additional stage between the ribosome recycling and translation initiation, at which the ribosome is main tained in a “preserved” state in the form of separate subunits, nontranslating 70S particles, or 100S dimers. The evolution of the ribosome hibernation has occurred within a very long period of time; ribosome hibernation is a conserved mechanism that is essential for maintaining the energy and resourceconsuming process of protein biosynthesis in organisms living in changing environment under stress conditions. DOI: 10.1134/S0006297920110115 Keywords: ribosome, translation, hibernation, silencing
BACTERIA ARE CONSTANTLY SUBJECTED TO STRESS In nature, microorganisms are subjected to the action of various stress factors, such as extreme tempera tures, extreme pH, drought, hypoxia, starvation, etc., to which bacterial cells respond by slowing down their growth, because the amounts of nutrients and electron donors/acceptors are usually low under such conditions [1]. Fast propagation of bacterial cultures in artificial growth media in a laboratory might be an artifact, since the growth conditions in this case are close to ideal. Nevertheless, even under these nearly ideal conditions, the growth of bacterial cultures occurs in six phases: lag Abbreviations: HPF, hibernation promoting factor; RaiA, ribo someassociated inhibitor A; RbfA, ribosomebinding factor A; RimM, ribosome maturation factor M; RimP, ribosome matu ration factor P; RMF, ribosome modulation factor; RsfS, ribo somal silencing factor. * To whom correspondence should be address
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