Figure 1.

circRNA biogenesis and function

circRNAs are mainly produced from gene transcripts by back-splicing. Based on their exonic and/or intronic source sequences, circRNA can be grouped into three major categories: exonic circRNAs (EciRNAs), exon-intron circRNAs (EIciRNAs), and intron-derived circRNAs (CiRNAs). circRNAs can interact with U1 small nuclear ribonucleoproteins (snRNPs) and polymerase II (Pol II) to promote gene transcription. circRNAs can reduce miRNA function by sponging miRNAs. circRNAs can regulate the function of proteins by working as protein decoys or scaffolds. circRNAs can be templates for translation to encode peptides, then produce proteins.