Figure 1.

The biogenesis of non-coding RNAs. (A) An immature miR transcript is transcribed and exported into the cytoplasm by Exportin 5 bound to Ran-GTP. The “guide” and “passenger” strands are created when the Dicer nuclease splits and processes these precursors. (B) The sequence of a lncRNA is transcribed by RNA polymerase II (PolII) and either spliced to its mature form or inefficiently spliced and retained in the nucleus. Alternatively, the sequence is transcribed by phosphorylation-dysregulated PolII, remains tethered to the chromatin, and either accumulates over time or is degraded. (C) CircRNAs are created through back-splicing mediated by RNA binding proteins, inverted repeat elements, or lariats created during mRNA splicing. The mature circRNA may contain only exons, only introns, or a combination of both. RBP: RNA-binding protein.