RNase 4 is a single-stranded RNA endonuclease that cleaves 3' of uridine in uridine-purine sequences (cut sites: U/A and U/G). RNase 4 allows more targeted digestion of substrate RNA material compared to single nucleotide specific RNases like T1 (cut site: after G), RNase U2 (cut sites: after A and G), or bovine pancreatic RNase A (cut sites: after C and U). RNase 4 endonuclease activity tolerates uridine base modifications such as pseudo-, N1-methyl-pseudo-, dihydro-, and 5-methoxy-uridine species. Due to the chemical mechanism of RNase 4 endonucleolytic cleavage, product oligonucleotides contain heterogenous 3' ends, where most species contain a linear 3'-phosphate or cyclic 2',3'-phosphate.