Characterization of a Novel GT-box Binding Protein from Arabidopsis.

Abstract

We isolated a cDNA encoding a novel GT-box binding protein from Arabidopsis, designated GT-4. The predicted open reading frame encodes a protein of 372 amino acids and the predicted protein sequence revealed the presence of a putative DNA-binding domain with 80% homology to the trihelix region of previously described light-responsive element binding protein, GT-1. Reverse transcription-PCR analysis showed that GT-4 transcripts are present in all tissues tested in light-grown plants, but light-regulated expression of GT-4 mRNA was observed only in etiolated seedlings. Electro-mobility shift assay using recombinant protein revealed that the GT-box-binding specificity of GT-4 is almost identical to that of GT-1. Transient expression of GT-4::GFP fusion protein in onion epidermal cells revealed the presence of a nuclear localization signal within the GT-4 protein. These results suggest the possibility that GT-4 is involved in GT-box-mediated gene expression by recognizing target sequences closely related to GT-1 binding sites.