AppppA and related adenylylated nucleotides are synthesized as a consequence of oxidation stress

AppppA , ApppGpp , AppppG , ApppG , and ApppA rapidly accumulate to high levels in Salmonella typhimurium following exposure to a variety of oxidizing agents, but not to a variety of other stresses. Among the agents inducing these adenylylated nucleotides are 1-chloro-2,4-dinitrobenzene, diamide, hydrogen peroxide, t-butyl hydroperoxide, N-ethyl maleimide, iodoacetamide, cadmium chloride, and a variety of quinones. Some of these oxidizing agents cause preferential synthesis of specific adenylylated nucleotides, e.g., N-ethyl maleimide induces ApppA and menadione induces ApppGpp . Our data, as well as other evidence in the literature, strongly suggest that oxidation stress is coupled to adenylylated nucleotide synthesis by aminoacyl-tRNA synthetases. Although adenylylated nucleotides are made by tRNA synthetases in vitro, their synthesis in vivo is not a simple consequence of inhibition of synthetase activity. Compounds that inhibit normal charging by aminoacyl-tRNA synthetases do not result in the synthesis of adenylylated nucleotides, nor do mutations in tRNA synthetase structural genes or tRNA structural, modifying, or processing genes. We propose that the family of adenylylated nucleotides are alarmones signaling the onset of oxidation stress, and that particular ones may be alarmones for specific oxidative stresses, e.g., ApppGpp for oxidative damage to amino acid biosynthesis.