Figure 1.

Amino acid sequence comparisons of various plant HOs. Identical and similar residues are in reverse type or gray boxes, respectively. The diamond identifies the predicted cleavage site for the chloroplast-transit peptide. The black triangles denote the beginning of the region in LeHO1 altered in the tomato yg-2^aud mutant and the T-DNA insertion site in Arabidopsis ho2-1. The black and white circles mark the histidines considered to be important for heme-iron binding and catalysis and for protein stability, respectively. Sequences include Arabidopsis (ectotype Col) AtHO1 (AF132475), AtHO2 (AF132475), AtHO3 (AF320022), and AtHO4 (AF320023); soybean GmHO1 (AF320024) and GmHO3 (AF320025); rice OsHO1 (C28969); sorghum SbHO1 (AF320026) and SbHO2 (AF320027); pine PtHO1 (AF320030); and tomato (cv Money-Maker) LeHO1 (AF320028) and LeHO2 (AF320029). The XXX in the sequences of GmHO1, GmHO3, and SbHO1 denotes the ends of the inferred polypeptide sequence from their truncated cDNAs.