Figure 1.

The main classification of circRNA. (a) With the interaction of TAFs (trans-acting factors), the cross-exon interactions are turned into cross-intron interactions and lead to the production of liner mRNA. (b) In the process of exon skipping, the cross-exon interactions are retained and ecircRNAs are formed. (c) The combination of the donor splice site and the acceptor splice site promotes the exon skipping. (d) Intron pairing is based on the interaction of complementary sequences or RBPs and their corresponding response elements in the long flanking intron; EIciRNAs, ecircRNAs, and ciRNAs are produced according to whether or not the introns are removed. (e) The C-rich and GU-rich elements present on opposite ends of the intron enhance the stability of intron and promote the formation of ciRNAs.