YdaT_toxin was first thought to be neutralised by the putative antitoxin YdaS (Pfam:PF15943) [1] but recent studies showed that both YdaS and YdaT can act independently as toxins and are regulated by RacR [2].

1: Regulation of growth and death in Escherichia coli by toxin-antitoxin systems. Yamaguchi Y, Inouye M; Nat Rev Microbiol. 2011;9:779-790. PMID:21927020

2: CRISPR-Cas-Mediated Gene Silencing Reveals RacR To Be a Negative Regulator of YdaS and YdaT Toxins in Escherichia coli K-12. Bindal G, Krishnamurthi R, Seshasayee ASN, Rath D; mSphere. 2017; [Epub ahead of print] PMID:29205229