AidB can repress its own synthesis during normal cell growth [1]. The crystal structure of AidB has been determined [2, 4] The purified N-terminal region of AidB (residues 1-439) has isovaleryl-CoA dehydrogenase activity but cannot bind DNA; the purified C-terminal region (residues 440-540) can bind DNA and functions as a transcriptional repressor in vivo but does not show isovaleryl-CoA dehydrogenase activity [1]. Overexpression of the aidB gene results in increased isovaleryl-CoA dehydrogenase activity in cell extracts [5] Overexpression also results in mutation rates which are less-than-wild-type after MNNG treatment [5] Some aidB lac fusions are less sensitive to alkylation damage than wild type [6, 7] An aidB mutant shows a wild-type adaptive response to alkylation treatment [6]and a wild-type adaptive response to H₂O₂ treatment with respect to protection against subsequent MNNG-induced damage [8] Expression of aidB is regulated by Ada in response to alkylation damage (primarily methylation) and involves interaction with RNA polymerase sigma factor Eσ⁷⁰ or Eσ^S [5, 6, 7, 9, 10, 11, 12, 13, 14, 15] Based on lac fusion experiments, expression ofaidB is induced by treatment with methyl methanesulfonate, MNNG, streptozotocin, and N-methyl-N-nitrosourea and shows growth phase regulation which is independent of ada [6, 16] Gene expression is induced under conditions of anaerobiosis [17]or acidification with acetate [18]and is dependent upon RpoS in these cases [19] Lrp is a repressor of aidB expression [20] cysA mutants block anaerobic induction of aidB while cysD, cysN, cysC, or cysH mutations increase anaerobic induction of aidB [21] aidB was induced by treatment with the sulfhydryl reagent N-ethylmaleimide [18] AidB has similarity to acyl coenzyme A dehydrogenases from mammals [5]. Reviews: [22, 23, 24, 25] AidB: "alkylation-inducible" [6]