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Mol Cell Endocrinol. 2006 Jun 27;252(1-2):2-10. Epub 2006 May 11.

Evolution of arylalkylamine N-acetyltransferase: emergence and divergence.

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Section on Neuroendocrinology, Office of the Scientific Director, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20894, USA.


The melatonin rhythm-generating enzyme, arylalkylamine N-acetyltransferase (AANAT) is known to have recognizable ancient homologs in bacteria and fungi, but not in other eukaryotes. Analysis of new cDNA and genomic sequences has identified several additional homologs in other groupings. First, an AANAT homolog has been found in the genome of the cephalochordate amphioxus, representing the oldest homolog in chordates. Second, two AANAT homologs have been identified in unicellular green algae. The homologs in amphioxus, unicellular green algae, fungi and bacteria are similarly primitive in that they lack sequences found in vertebrate AANATs that are involved in regulation and that facilitate binding and catalysis. In addition, all these sequences are intronless. These features are consistent with horizontal transfer of the AANAT ancestor from bacteria to green algae, fungi and chordates. Lastly, a third AANAT gene has been found in teleost fish, suggesting that AANAT genes serve multiple functions in addition to melatonin synthesis.

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