Toxic component of a type II toxin-antitoxin (TA) system. An endoribonuclease that cleaves 23S rRNA in the sarcin-ricin loop (SRL). The SRL sequence is highly conserved and is implicated in GTP hydrolysis by EF-Tu and EF-G. Acts on purified ribosomes but not on isolated RNA. Its toxic effect is neutralized by coexpression with cognate antitoxin VapB20. Belongs to the PINc/VapC protein family.