Toxic component of a type II toxin-antitoxin (TA) system. Probably exerts its toxic effect by binding to mRNA, inhibiting translation. Binds to, recognizes and cleaves ssRNA at ACGC and AC(A/U)GC sequences, usually between the G and C; cleavage is not very efficient, nor is cleavage required to inhibit protein synthesis. Upon expression in situ, in M.smegmatis or E.coli inhibits cell growth and colony formation; in at least E.coli also causes increased levels of cellular RNA. Its toxic effect is neutralized by coexpression with cognate antitoxin VapB4