Figure 2. Two different models of exon circularization of circRNA.

(A) Intron-pairing-driven circularization: during the formation of circRNA, an intron reverse complementary motif comprising GU-rich and C-rich elements is the key component to facilitate cyclization. (B) Lariat-driven circularization: the formation of circRNA is facilitated by the lariat structure. The complementary ALU flanking element which is repeated in the intron region competing for classical linear RNA splicing and the circularization is accelerated by reverse complementarity.