Fig. 4. HAP2 and its predicted protein structure. (A) HAP2 has 17 exons (black rectangles, untranslated regions are gray). hap2-1, hap2-2 and gcs1 (Mori et al., 2006) are T-DNA insertions in exons 15, 9 and 16, respectively. Black lines under the gene schematic indicate regions used for molecular complementation (HAP2tr), analysis of expression pattern (HAP2promoter:YFP) and subcellular localization (HAP2protein:YFP). (B) HAP2 encodes a 705 amino acid protein with a predicted 19 amino acid N-terminal signal sequence (S), a 23 amino acid transmembrane domain (T) and a C-terminus containing a 96 amino acid histidine-rich domain (HIS). (C) An alignment of the HAP2 HIS-rich region from Arabidopsis (A. thaliana), poplar (P. trichocarpa), lily (L. longiflorum) (Mori et al., 2006) and rice (O. sativa). The alignment includes the region of the HAP2 C-terminal to the transmembrane domain. HIS residues within the HIS-rich region are shaded gray. Conserved residues are indicated with a star. Conservative amino acid substitutions are indicated with a dot. (D) Pairwise analysis of amino acid identity between Arabidopsis HAP2 and HAP2 sequences from other organisms; only HAP2 sequences from angiosperms have a C-terminal HIS-rich region.