Modifications of ribosomal RNA: From enzymes to function

Abstract

Modified nucleosides are present in all kinds of stable RNA molecules, tRNAs being particularly rich in them (Auffinger and Westhof, 1998). Ribosomal RNA (rRNA) from all organisms contains modifications, and there is a correlation between the overall complexity of an organism and the number of modified nucleosides in its rRNA. The rRNA of the most primitive bacteria, such as some Mycoplasma species, may possess only 14 modified nucleosides (de Crécy-Lagard et al., 2007). In Escherichia coli, there are 36 modified nucleosides in rRNA (Table I). Yeast ribosomes possess about one hundred rRNA modifications, human rRNA over two hundred (Ofengand and Fournier, 1998; Decatur and Fournier, 2002). Eukaryotes and archaea use snoRNA guided rRNA modification mechanism. This mechanism allows archaea and eukarya to use a limited number of modification enzymes, mainly pseudouridine synthase and 2{\textasciiacutex}-O-methyltransferase to introduce the majority of their rRNA modifications (Decatur and Fournier, 2002). By contrast, bacteria have developed specific enzymes for each one of the (fewer) modifications they have. Nevertheless, there are many different rRNA modifications in bacteria. Despite intensive study for several decades, many open questions remain regarding the functional role of modified rRNA nucleosides. In this review we will focus on rRNA modifications in E. coli and discuss their possible functions.