Toxic component of a type II toxin-antitoxin (TA) system (PubMed:19016878, PubMed:24225902). An endoribonuclease that cleaves both E.coli and M.smegmatis 23S rRNA between G2661 and A2662 in the sarcin-ricin loop (SRL, E.coli 23S rRNA numbering). 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 in E.coli, nor on a shortened artificial substrate (PubMed:24225902). Upon expression in E.coli inhibits cell growth, colony formation and translation. Its toxic effect is neutralized by coexpression, or subsequent expression (tested over 2 hours) with cognate antitoxin VapB20 (PubMed:19016878, PubMed:24225902). Inhibited by EDTA. Belongs to the PINc/VapC protein family.