Conservation of two distinct types of 100 S ribosome in bacteria

In bacteria, 70S ribosomes (consisting of 30S and 50S subunits) dimerize to form 100S ribosomes, which were first discovered in E scherichia coli . Ribosome modulation factor ( RMF ) and hibernation promoting factor ( HPF ) mediate this dimerization in stationary phase. The 100 S ribosome is translationally inactive, but it dissociates into two translationally active 70 S ribosomes after transfer from starvation to fresh medium. Therefore, the 100 S ribosome is called the ‘hibernating ribosome’. The gene encoding RMF is found widely throughout the G ammaproteobacteria class, but is not present in any other bacteria. In this study, 100 S ribosome formation in six species of G ammaproteobacteria and eight species belonging to other bacterial classes was compared. There were several marked differences between the two groups: (i) Formation of 100S ribosomes was mediated by RMF and short HPF in G ammaproteobacteria species, similar to E . coli , whereas it was mediated only by long HPF in the other bacterial species; (ii) RMF /short HPF ‐mediated 100 S ribosome formation occurred specifically in stationary phase, whereas long HPF ‐mediated 100 S ribosome formation occurred in all growth phases; and (iii) 100 S ribosomes formed by long HPF were much more stable than those formed by RMF and short HPF .