A novel type of dimerization motif, related to leucine zippers, is present in plant homeodomain proteins.
Sunflower HAHR1 is a homeodomain protein presumably involved in some aspects of root development. In the present work, we have studied the oligomerization properties of HAHR1. A protein containing the entire homeodomain plus adjacent C-terminal sequences (amino acids 86-325) behaves as a dimer in gel filtration experiments. When a fragment C-terminal to the homeodomain (amino acids 151-263) is fused to the N-terminal domain of the lambda phage repressor, it is able to confer binding efficiency to this domain, as judged by protection from lambda superinfection and repression of beta-galactosidase expression under the control of the P(R) promoter. A smaller fragment (amino acids 151-184) confers only conditional repression. GSH transferase fusion proteins containing the entire homeodomain of HAHR1 plus the above-mentioned adjacent sequences bind with similar efficiency a mixture of oligonucleotides selected from a random population. The smaller protein, however, loses its binding capacity when separated from the GSH transferase moiety. Retention of a labelled HAHR1 protein synthesized in vitro by GSH transferase fusions containing different protein fragments adjacent to the homeodomain and bound to GSH agarose suggests that a portion from amino acids 151-263 is required for efficient interaction. The results obtained indicate that HAHR1 interacts with DNA as a dimer and that its dimerization domain is located immediately C-terminal to the homeodomain. We define two regions, the first of which confers non-efficient dimerization; this region would be stabilized by the presence of the second one through putative mutual interactions. A similar motif is present in other related plant homeodomain proteins.
Palena
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CM
Area Biología Molecular, Facultad de Ciencias Bioquímicas y Farmacéuticas (UNR) and Programa Multidisciplinario de Biología Experimental (PROMUBIE, CONICET), Suipacha, Rosario, Argentina.
Chan
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RL
Gonzalez
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DH
D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016350:Leucine Zippers / Q000235:genetics*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
D018398:Homeodomain Proteins; D010940:Plant Proteins