Sequencing, phylogenetic and transcriptional analysis of the glyoxylate bypass operon (ace) in the halophilic archaeon Haloferax volcanii

The glyoxylate cycle occurs in the three domains of living organisms: Eukar ya, Bacteria and Archaea. We have isolated and sequenced the ace (acetate a ssimilation) gene operon, comprising the glyoxylate cycle key enzymes isoci trate lyase and malate synthase genes (icl or aceA and ins or aceB), from t he halophilic archaeon Haloferax volcanii. This is the first time that thes e genes are sequenced in an organism from the domain Archaea. Phylogenetic analysis of the sequenced genes revealed that isocitrate lyase shows a sign ificant identity with isocitrate lyases from Eukarya and Bacteria, but it i s not more closely related to eukaryal or bacterial enzymes, and that malat e synthase from H. volcanii has very little identity with any other known p rotein. This enzyme forms a new class of malate synthases. Transcriptional analysis indicated that both genes are cotranscribed in a single 2.7 kb mRN A molecule. The genes were transcribed only when acetate was the carbon sou rce, indicating transcriptional regulation. Two sets of palindromic sequenc es were found in the promoter region, possibly involved in binding of trans criptional regulators (repressors and/or activators). (C) 2001 Elsevier Sci ence B.V. All rights reserved.