Fig. 1: Biosynthesis and metabolism of circRNA.
From: CircRNAs in colorectal cancer: potential biomarkers and therapeutic targets
A Possibility of looped structures generation either by base-pairing among complementary sequences that flank the circularized exons or via RBPs. To generate EcRNAs and EIciRNAs, the intron sequences can be deleted or kept respectively in the loop structure. B The exon-skipping events generate certain EcRNAs, whereas a lariat is internally spliced to remove intronic sequences. C The intron-containing pre-tRNA is cleaved at the BHB motif into half of the exon and intron part. A mature tRNA is formed by joining the halves of the exons, and a tricRNA is produced by joining the termini of the introns. D miRNA directly binds at the AGO2-dependant cleavage site of targeted mRNA molecules in a complementary way. E RNase mitochondrial RNA processing (RNase MRP) promotes the cleavage of m6A-possessing circRNAs via the activities of YTHDF2 and HRSP12. F When infected by viruses, active RNase L degrades circRNA. AGO2 argonaute 2, BHB motif bulge-helix-bulge motif, ciRNA circular intronic RNA, EcRNAs exonic circRNAs, EIciRNAs exon-intron circRNAs, RBP RNA-binding protein, YTHDF2 YT521-B homology domain family 2, tricRNA tRNA intronic circular RNA.
