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The Highly Similar Arabidopsis Homologs of Trithorax ATX1 and ATX2 Encode Proteins with Divergent Biochemical Functions^[W]

^a School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588-0118
^b North Carolina State University, Raleigh, North Carolina 27606
^c Department of Genetic Engineering, Centro de Investigación y de Estudios Avanzados, Campus Guanajuato, Irapuato, C.P. 36821, Mexico
^d Department of Cell and Molecular Biology, Boston University, Boston, Massachusetts 02215
^e Microscopy Facility, Appalachian State University, Boone, North Carolina 28608
^f Faculty of Agriculture, University of Jordan, Amman 11942, Jordan
^g Genomics Core Research Facility, Center for Biotechnology, University of Nebraska, Lincoln Nebraska 68588-0665
^h Department of Biology, University of Nebraska, Omaha, Nebraska 68182-0040
ⁱ Center for Biotechnology and Department of Statistics, University of Nebraska, Lincoln, Nebraska 68588-0665

¹ Address correspondence to zavramova2{at}unl.edu.

Gene duplication followed by functional specialization is a potent force in the evolution of biological diversity. A comparative study of two highly conserved duplicated genes, ARABIDOPSIS TRITHORAX-LIKE PROTEIN1 (ATX1) and ATX2, revealed features of both partial redundancy and of functional divergence. Although structurally similar, their regulatory sequences have diverged, resulting in distinct temporal and spatial patterns of expression of the ATX1 and ATX2 genes. We found that ATX2 methylates only a limited fraction of nucleosomes and that ATX1 and ATX2 influence the expression of largely nonoverlapping gene sets. Even when coregulating shared targets, ATX1 and ATX2 may employ different mechanisms. Most remarkable is the divergence of their biochemical activities: both proteins methylate K4 of histone H3, but while ATX1 trimethylates it, ATX2 dimethylates it. ATX2 and ATX1 provide an example of separated K4 di from K4 trimethyltransferase activity.