A new paper from the Grzechnik lab (Cells & Molecules research area) published in Nature Communications reveals another mechanism differentiating synthesis of non-coding and coding RNA.
In all eukaryotic cells, RNA Polymerase II (Pol II) generates messenger RNA (mRNA) and various non-coding transcripts (ncRNA). Both RNA classes are initially capped at the 5’ end and polyadenylated at the 3’ end. However, in contrast to mRNA which is exported to cytoplasm and translated, most of ncRNA retain in the nucleus and are subjected for nucelolytic pathways. Since many ncRNA may regulate gene expression, is of central importance to understand how ncRNA synthesis is controlled and how this process differs from mRNA maturation.
Researchers from the University of Birmingham, University of Oxford and University of Warsaw used a model organism Saccharomyces cerevisiae to study maturation of small nucleolar RNA (snoRNA), essential ncRNA class involved in ribosome biogenesis. Employing genome wide and single-gene approaches, the scientist discovered that cap structure is removed from snoRNA precursor while Pol II is still transcribing the snoRNA gene. The team revealed that this process is essential for snoRNA exonucleolytic maturation, nuclear localization and ultimately, snoRNA functions in ribosome synthesis. Thus, co-transcriptional cap removal has emerged as one of the major factors directing snoRNA for ncRNA-specific maturation pathways.
Model for box C/D snoRNA maturation in yeast. Co-transcriptional cleavage mediated by Rnt1 removes the cap structure from box C/D pre-snoRNA and so directs the precursor to the snoRNP synthesis pathway in WT cells. In the rnt1Δ strain, retained m7G cap marks the RD box C/D pre-snoRNA as mRNA resulting in cytoplasmic localization of 5ʹ and 3ʹunprocessed snoRNA