A novel type of dimerization motif, related to leucine zippers, is present in plant homeodomain proteins

PALENA, CLAUDIA M.; CHAN, RAQUEL L.; GONZALEZ, DANIEL H.

BIOCHIMICA ET BIOPHYSICA ACTA, N. GENE STRUCTURE AND EXPRESSION

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Lugar: Amsterdam; Año: 1997 vol. 1352 p. 203 - 212

0167-4781

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 β-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 hind 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.