Pseudouridine-Free Escherichia coli Ribosomes

Pseudouridine (psi) is present at conserved, functionally important regions in the ribosomal RNAs (rRNAs) from all three domains of life. Little, however, is known about the functions of psi modifications in bacterial ribosomes. An Escherichia coli strain has been constructed in which all seven rRNA psi synthases have been inactivated and whose ribosomes are devoid of all psi s. Surprisingly, this strain displays only minor defects in ribosome biogenesis and function, and cell growth is only modestly affected. This is in contrast to a strong requirement for psi in eukaryotic ribosomes and suggests divergent roles for rRNA psi modifications in these two domains. IMPORTANCE Pseudouridine (psi) is the most abundant posttranscriptional modification in RNAs. In the ribosome, psi modifications are typically located at conserved, critical regions, suggesting they play an important functional role. In eukarya and archaea, rRNAs are modified by a single pseudouridine synthase (PUS) enzyme, targeted to rRNA via a snoRNA-dependent mechanism, while bacteria use multiple stand-alone PUS enzymes. Disruption of psi modification of rRNA in eukarya seriously impairs ribosome function and cell growth. We have constructed an E. coli multiple deletion strain lacking all psi modifications in rRNA. In contrast to the equivalent eukaryotic mutants, the E. coli strain is only modestly affected in growth, decoding, and ribosome biogenesis, indicating a differential requirement for psi modifications in these two domains.