Fig. 1

Biogenesis of ecircRNAs and EIciRNAs. a Intron-pairing-driven circularization: The introns flanking inverted repeats or ALU elements form a circular RNA by base pairing, and ecircRNAs or EIciRNAs are formed by removing or retaining introns. b Lariat-driven circularization: EcircRNAs or EIciRNAs are generated by exon skipping. Exons 5′ attacks the 3′ splice site, forming an RNA lariat containing skipped exons 2 and 3 and an mRNA consisting of exon 1 and exon 4. Then, an EIciRNA and an RNA double lariat were further formed. c circRNA biogenesis depends on RBPs: RBPs bind to the sequence motifs of upstream and downstream introns, which serve as a bridge to bring flanking introns closer to each other, promoting the formation of circRNAs