Toxic component of a toxin-immunity protein module, which functions as a cellular contact-dependent growth inhibition (CDI) system. A site-specific tRNA3(Ser) nuclease, the C-terminus (residues 2201-2335) probably removes 2 or 4 nucleotides from the 3' end of tRNA3(Ser) but not tRNA2(Arg) or tRNA(Glu) (upon expression in E.coli), possibly endonucleolytically. The nuclease activity is neutralized by expression of the cognate immunity protein WapI from the same strain, but not its homolog from 2 other B.subtilis strains. The C-terminus cannot be expressed on its own in E.coli, however it can be cloned in the presence of its cognate immunity protein gene wapI. Cell contact is probably necessary for growth inhibition. Released into the medium. Belongs to the RHS/WapA nuclease family.