RNase R (Ribonuclease R) is a 3 '-5' exonuclease derived from the Escherichia coli RNR superfamily that progressively cuts RNA into dinucleotides and trinucleotides from the 3 '-5' direction. RNase R can digest almost all linear RNA molecules, but it is difficult to digest circular RNA, lasso structures, or double-stranded RNA molecules with fewer than seven nucleotides at the 3' protruding end. RNase R is an essential tool enzyme for circRNA identification and enrichment experiments, digesting linear RNA to enrich for circular RNAs (circRNAs) or lasso-structured RNAs (lariat RNAs).