[RNA] containing adenosine + H2O = an [RNA fragment]-3'-adenosine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA fragment]. [RNA] containing guanosine + H2O = an [RNA fragment]-3'-guanosine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA fragment]. After treatment by base Asn-32 and Asp-45 partially isomerise by succinimide rearrangement to form iosaspartyl peptides. Belongs to the ribonuclease U2 family.