Figure 2.

Generation of circRNAs from lariats. Lariats are lasso-shaped molecules that originate from pre-mRNAs during both alternative splicing and linear splicing. Lariats are formed when a 5′ end of a spliced intron is joined with a covalent bond to the BP adenosine of the intron. The lariat can either be linearized by specific RNA lariat debranching enzymes and thus be degraded, or escape debranching and form a stable circular transcript upon trimming of the 3′ linear tail. When lariats originate from linear splicing, they only contain introns and if they escape debranching, they produce Intronic circRNAs. However, lariats can also originate from alternative splicing, and therefore contain alternative exons together with the introns. Back splicing of hybrid exon-intron lariats generates Exonic circRNA.