Fig 4.

Gene cluster encoding enzymes possibly involved in acetone degradation in A. aromaticum. The acxABC genes encode the three subunits of acetone carboxylase. The gene product of ebA4717 (labeled CoA Lig) shows similarity with known CoA ligases and may be the enzyme activating acetoacetate to acetoacetyl-CoA (Fig. 2). Alternatively, this reaction may be catalyzed by KctAB (labeled TF), which show sequence similarities to the subunits of succinyl-CoA:3-ketoacid-CoA transferases. The gene product of ebA4705 shows similarities to putative exporters of the RND superfamily (transporter class TC no. 2.6; tcdb.org). Open reading frames ebA4709, ebA4715, and ebA4720 code for putative proteins of unknown function. Gene ebA4712 encodes a putative LysR-like regulator. The gene acxR codes for a sigma 54-dependent transcriptional activator. Genes for similar sigma 54-dependent regulator proteins are also present in acetone metabolic gene clusters of other bacteria (22), while the other open reading frames are not conserved on a widespread basis. hyp., hypothetical protein; Reg., putative regulatory protein.