The two homeodomains of the ZmHox2a gene from maize originated as an internal gene duplication and have evolved different target site specificities.
The maize ZmHox2a gene encodes two homeodomains which originated by a 699 bp duplication within an ancestral precursor. The sequences of the two ZmHox2a homeodomains are highly diverged in the N-terminal arm, while residues in the helical part have mostly been conserved. We show here that both ZmHox2a homeodomains are functional DNA-binding motifs but exhibit different target site specificities. CASTing experiments reveal a TCCT motif recognized by HD1 but a GATC tetranucleotide as the recognition sequence of HD2. Mutation of the central nucleotides in both tetranucleotide core motifs abolishes DNA binding. A domain swap experiment indicates that target site specificity is achieved in a combinatorial manner by the contributions of the diverged N-terminal arms together with the slightly different recognition helices. Computer modelling suggests that K47 and H54 in the recognition helices preferentially contact the bases at the 3'-terminus of the tetranucleotide target sequences.
Kirch
T
T
Institut für Entwicklungsbiologie and Institut für Genetik, Universität zu Köln, Gyrhofstrasse 17, 50923 Köln, Germany.
Bitter
S
S
Kisters-Woike
B
B
Werr
W
W
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D003198:Computer Simulation; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D020440:Gene Duplication; D005801:Genes, Homeobox; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000096:biosynthesis / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000302:isolation & purification; D013379:Substrate Specificity; D003313:Zea mays / Q000235:genetics* / Q000378:metabolism
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C098999:Hox2a protein, Zea mays; D009838:Oligodeoxyribonucleotides; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins