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. 2022 Mar 1;2:834655. doi: 10.3389/fbinf.2022.834655

FIGURE 1.

FIGURE 1

CircRNAs formation and primer design. (A) CircRNAs are formed through a process called back-splicing, which results in a covalently closed loop characterized by a back-splice junction (BSJ). (B) CircRNA-specific primers amplify the region surrounding the BSJ when annealing to the circRNA (convergent orientation). These primers will not amplify linear RNA (divergent orientation). (C) First, CIRCprimerXL retrieves the sequence surrounding the circRNA BSJ (step 1). Next, both common SNPs and regions with secondary structures are flagged (step 2) and avoided during primers design (step 3). Finally, the primers are filtered based on their specificity and secondary structures in the amplicon (step 4).