Figure 3.

Functions of circular RNAs. In the cytoplasm, circRNAs can interact with miRNA-Ago2 complexes to inhibit miRNA action on linear targets (A). Additionally, circRNAs can interact with RNA-binding proteins (RBPs) as can linear RNAs and may either facilitate interaction between RBPs to inactivate/activate them (B) or sequester these to prevent them from functioning (C). In the nucleus, (D) circRNAs with retained introns can promote transcription of their parental gene by interacting with RNA polymerase II (Pol II) and U1 snRNP at the promoter of the gene. (E) During splicing, the elements facilitating backsplicing and linear splicing compete with each other. As a result of this competition either a linear RNA or an alternatively spliced linear RNA and a circRNA is generated. Hence, the backsplicing pattern may alter the expression of the linear gene product.