Published on Aug. 1, 2014 in J Biol Chem volume None.
PubMed ID: 25086048
Biogenesis of eukaryotic ribosome is a complex event involving a number of non-ribosomal factors. During assembly of the ribosome, rRNAs are post-transcriptionally modified by 2 -O-methylation, pseudouridylation, and several base-specific modifications, which are collectively involved in fine-tuning translational fidelity and/or modulating ribosome assembly. By mass-spectrometric analysis, we demonstrated that N4-acetylcytidine (ac4C) is present at position 1773 in the 18S rRNA of Saccharomyces cerevisiae. In addition, we found that an essential gene, KRE33 (human homolog, NAT10), which we renamed RRA1 (Ribosomal RNA cytidine Acetyltransferase 1) encoding an RNA acetyltransferase responsible for ac4C1773 formation. Using recombinant Rra1p, we could successfully reconstitute ac4C1773 in a model rRNA fragment in the presence of both acetyl-CoA and ATP as substrates. Upon depletion of Rra1p, the 23S precursor of 18S rRNA was accumulated significantly, which resulted in complete loss of 18S rRNA and small ribosomal subunit (40S), suggesting that ac4C1773 formation catalyzed by Rra1p plays a critical role in processing of the 23S precursor to yield 18S rRNA. When nuclear acetyl-CoA was depleted by inactivation of Acetyl CoA Synthetase 2 (ACS2), we observed temporal accumulation of the 23S precursor, indicating that Rra1p modulates biogenesis of 40S subunit by sensing nuclear acetyl-CoA concentration.