Toxic component of a type II toxin-antitoxin (TA) system (PubMed:24923448). A sequence-specific mRNA endoribonuclease that inhibits translation elongation and induces bacterial stasis (Probable). Cleavage occurs between the second and third residue of the Lys codon followed by a G or A (5'AAA(G/A)3'), is reading-frame dependent and occurs within the 5' end of most mRNAs (By similarity). Ribosome-binding confers the sequence specificity and reading frame-dependence (By similarity). The YafQ-DinJ heterotetramer binds the consensus sequence 5'-TTTGAGCTACA-3' in the dinJ promoter; DinJ also binds DNA but not as well as the YafQ-DinJ complex (PubMed:24923448). Monomer in solution, forms a heterotetramer with antitoxin DinJ, with 2 YafQ-DinJ dimers associated via the N-terminus of the DinJ antitoxins (YafQ-(DinJ)2-YafQ) (PubMed:24923448). Belongs to the RelE toxin family. YafQ subfamily.