YdaS is a transcription factor found in the cryptic prophage Rac of E. coli K12 and represents a novel family within the HigA superfamily as it is distantly related to HigA antitoxins. YdaS can act as a toxin whose expression is regulated by RacR and behaves as a monomer in solution [2,3]. Previously, it was thought to be an antitoxin that neutralises the toxin YdaT [3].

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: (1)H, (13)C, and (15)N backbone and side chain chemical shift assignment of YdaS, a monomeric member of the HigA family. Prolic-Kalinsek M, De Bruyn P, Jurenas D, Van Melderen L, Loris R, Volkov AN; Biomol NMR Assign. 2020;14:25-30. PMID:31625047

3: 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