Antitoxin component of a type II toxin-antitoxin (TA) system (PubMed:17263853). A labile antitoxin that counteracts the effect of cognate toxin YafQ (PubMed:17263853). YafQ and DinJ together bind their own promoter, and repress its expression (PubMed:24898247). There are 2 operators with imperfect inverted repeats (IR) in the dinJ promoter, YafQ-(DinJ)2-YafQ only binds to the first (most upstream) of them to repress transcription; binding to a single IR is sufficient for activity in vivo and in vitro (PubMed:24898247). DinJ alone is as potent a transcriptional repressor as the heterotetramer and also only needs to bind 1 IR to act (PubMed:24898247). Cell death governed by the MazE-MazF and DinJ-YafQ TA systems seems to play a role in biofilm formation (PubMed:19707553). 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:17263853, PubMed:24898247). In this complex the toxin activity is inhibited. Not induced by the DNA damaging agent mitomycin C (PubMed:19210620). Transcription is autorepressed by DinJ or YafQ-(DinJ)2-YafQ via operator 1, repressed by LexA via operator 2 (PubMed:24898247). Probably degraded by the Lon and ClpPX proteases in vivo. Cells missing dinJ-yafQ have reduced biofilm formation. Belongs to the RelB/DinJ antitoxin family.