Fig. 1

Biogenesis and function of circRNAs. A. The flanking introns of circularized exons contain reverse complementary sequences, which form a circular structure through direct base pairing, or RBP binding sites, which generate a circular structure via RBPs dimerization. The introns are removed or retained to form exonic circRNA (ecircRNA) or exon-intron circRNA (EIciRNA). Intronic circRNA (ciRNA) is derived from an intron by preventing intron debranching after splicing. Mitochondria encoded circRNAs (mecciRNAs) probably circularize via a splicing-independent mechanism. B. CircRNAs serving as miRNA sponges. C. CircRNAs promoting the transcription of targets through interacting with proteins or complexes such as U1 snRNP. D. CircRNAs behaving as protein decoys. E. CircRNAs working via generating polypeptides