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Fig. 2 | Journal of Hematology & Oncology

Fig. 2

From: Function and clinical significance of circRNAs in solid tumors

Fig. 2

Biogenesis of circRNAs from introns and intergenic circRNAs. a ciRNA: The pre-mRNA is spliced to produce an RNA lariat with a 2′,5′-phosphodiester, and the ciRNA is formed upon removal of the 3′-tail. b Excised group I introns: Exogenous guanosine (G) attacks the 5′-terminus of the intron, and exon 1 is cleaved due to transesterification. Then, the 5′-terminus of exon 2 is attacked by the 3′-hydroxyl of free exon 1, creating a linear intron. The 2′-hydroxyl close to the 3′-terminus of this linear intron attacks the phosphodiester bond near the 5′-terminus, resulting in an RNA lariat with 2′,5′-phosphodiester and a released 5′-terminus sequence. After removing the 3′-tail of the RNA lariat, a circRNA from group I introns is formed. c Excised group II introns: Pre-mRNA releases exon 2, and the 2′-hydroxyl of the intron’s 3′-terminus attacks the phosphodiester bond near the 5′-terminus, producing an RNA lariat with 2′,5′-phosphodiester and the free exon 1. d The circRNA contains two ICFs flanked by GT-AG splicing signals which act as SD and SA of the circular junction to form an integrated circRNA

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