| Summary: | <p>Abstract</p> <p>Background</p> <p>Aminoadipate reductase (Lys2) is a fungal-specific protein. This enzyme contains an adenylating domain. A similar primary structure can be found in some bacterial antibiotic/peptide synthetases. In this study, we aimed to determine which bacterial adenylating domain is most closely related to Lys2. In addition, we analyzed the substitution rate of the adenylating domain-encoding region.</p> <p>Results</p> <p>Some bacterial proteins contain more than two similar sequences to that of the adenylating domain of Lys2. We compared 67 amino acid sequences from 37 bacterial and 10 fungal proteins. Phylogenetic trees revealed that the <it>lys2 </it>genes are monophyletic; on the other hand, bacterial antibiotic/peptide synthase genes were not found to be monophyletic. Comparative phylogenetic studies among closely related fungal <it>lys2 </it>genes showed that the rate of insertion/deletion in these genes was lower and the nucleotide substitution rate was higher than that in the internal transcribed spacer (ITS) regions.</p> <p>Conclusions</p> <p>The <it>lys2 </it>gene is one of the most useful tools for revealing the phylogenetic relationships among fungi, due to its low insertion/deletion rate and its high substitution rate. Lys2 is most closely related to certain bacterial antibiotic/peptide synthetases, but a common ancestor of Lys2 and these synthetases evolutionarily branched off in the distant past.</p>
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