Schematic representation of the AtRH (A),CeRH (B), and DmRH (C) gene structures. Boxes represent exons and lines introns. Lengths are roughly at scale. (Gray) Regions coding for catalytic domains; (white) regions encoding the amino- and carboxy-terminal ends (see Aubourg et al. 1999 for a representation of 32 AtRH protein primary structures). The conserved intron positions are numbered starting from thetop. Classes based on the conservation of the structures of the genes (see text for details) are separated by an alternative shading. Large CeRH and DmRH genes are on several lines and broken lines have been used in large introns that are not drawn to scale.