C/D box sRNA-guided 2′-O-methylation patterns of archaeal rRNA molecules

Patrick P. Dennis, Vanessa Tripp, Lauren Lui, Todd Lowe, Lennart Randau

In archaea and eukaryotes, ribonucleoprotein complexes containing small C/D box s(no)RNAs use base pair complementarity to target specific sites within ribosomal RNA for 2'-O-ribose methylation. These modifications aid in the folding and stabilization of nascent rRNA molecules and their assembly into ribosomal particles. The genomes of hyperthermophilic archaea encode large numbers of C/D box sRNA genes, suggesting an increased necessity for rRNA stabilization at extreme growth temperatures. We have identified the complete sets of C/D box sRNAs from seven archaea using RNA-Seq methodology. In total, 489 C/D box sRNAs were identified, each containing two guide regions. A combination of computational and manual analyses predicts 719 guide interactions with 16S and 23S rRNA molecules. This first pan-archaeal description of guide sequences identifies (i) modified rRNA nucleotides that are frequently conserved between species and (ii) regions within rRNA that are hotspots for 2'-O-methylation. Gene duplication, rearrangement, mutational drift and convergent evolution of sRNA genes and guide sequences were observed. In addition, several C/D box sRNAs were identified that use their two guides to target locations distant in the rRNA sequence but close in the secondary and tertiary structure. We propose that they act as RNA chaperones and facilitate complex folding events between distant sequences. This pan-archaeal analysis of C/D box sRNA guide regions identified conserved patterns of rRNA 2'-O-methylation in archaea. The interaction between the sRNP complexes and the nascent rRNA facilitates proper folding and the methyl modifications stabilize higher order rRNA structure within the assembled ribosome.