YaaA is a key element of the stress response to H2O2. It acts by reducing the level of intracellular iron levels after peroxide stress, thereby attenuating the Fenton reaction and the DNA damage that this would cause [1]. The molecular mechanism of action is not known.

1: The YaaA protein of the Escherichia coli OxyR regulon lessens hydrogen peroxide toxicity by diminishing the amount of intracellular unincorporated iron. Liu Y, Bauer SC, Imlay JA; J Bacteriol. 2011;193:2186-2196. PMID:21378183