GT-2: a transcription factor with twin autonomous DNA-binding domains of closely related but different target sequence specificity.

Abstract

A triplet of adjacent, highly similar GT motifs in the phyA promoter of rice functions to support maximal expression of this gene. We have obtained a recombinant clone that encodes a full‐length nuclear protein, designated GT‐2, which binds specifically to these target sequences. This novel protein contains acidic, basic and proline‐ + glutamine‐rich regions, as well as two autonomous DNA‐binding domains, one NH2‐terminal and the other COOH‐terminal, that discriminate with high resolution between the three GT motifs. A duplicated sequence of 75 amino acids, present once in each DNA‐binding domain, appears likely to mediate DNA target element recognition. Each copy of this duplicated protein sequence is predicted to form three amphipathic alpha‐helices separated from each other by two short loops. The absence of sequence similarity to other known proteins suggests that this predicted structural unit, which we term the trihelix motif, might be representative of a new class of DNA‐binding proteins.

Molecular dissection of GT-1 from Arabidopsis.

“…The nucleotide sequence data of Arabidopsis GT-1 are available in EMBL, GenBank, and DDBJ nucleotide sequence data bases as accession number L36806. Putative trihelices of tobacco GT-lalB2F (amino acids 75 to 138; Gilmartin et al, 1992), Arabidopsis GT-1 (amino acids 87 to 150; this study), Arabidopsis GT-2 (amino acids 81 to 161 and amino acids 437 to 512; Kuhn et al, 1993), and rice GT-2 (amino acids 98 to 175 and amino acids 489 to 564; Dehesh et al, 1992) are indicated. The degree of homology between the trihelices is shown.…”

“…This observation prompted us to investigate the binding activity of the recombinant Arabidopsis GT-1 to various GT-related motifs. Figure 4 shows the results of gel shifts using probes of tetramers of rbcS-3A box III (Sarokin and Chua, 1992) and the rice PHYA GT2 box and GT3 box (Dehesh et al, 1992). The full-length B E H P Arabidopsis DNA (1 ng) digested with BamHI, EcoRI, Hindlll, andPstl was electrophoresed in lanes B, E, H, and R respectively, and probed with a radiolabeled Bglll-and EcoRI-digested Arabidopsis GT-1 cDNA fragment.…”

“…The predicted secondary structure suggested the presence of a putative trihelix motif contained within the region from Trp-87 to Lys-150. This region showed the highest homology not only to the tobacco GT-la/B2F putative trihelix region (Gilmartin et al, 1992;Perisic and'lam, 1992), but also to the putative trihelices of GT-2 from Arabidopsis (Kuhn et al, 1993) and rice (Dehesh et al, 1992) (Figure 2). …”

Ancestral Multipartite Units in Light-Responsive Plant Promoters Have Structural Features Correlating with Specific Phototransduction Pathways

“…A number of these elements are found in both PhANG and PheMAGs promoters, and some of them have been proposed to be involved in light regulation . However, several studies have shown that deletion or mutation of GT-1 sites do not affect the photoresponsiveness of some PhANG promoters (reviewed by Terzaghi and Cashmore, 1995), and it has been established that GT-1 elements that were found in bean chs25 and rice phyA promoters function as silencers and constitutive activating elements, respectively (Lawton et al, 1991;Dehesh et al, 1992). Moreover, it has been reported that GT-1-like factors interact with nonphotoresponsive promoters (Buchel et al, 1996).…”

Light-regulated modification and nuclear translocation of cytosolic G-box binding factors in parsley.

“…In some instances, it has been shown that these elements are involved in the light responsiveness of the genes and can be occupied by protein factors. In the case of the cabE gene, many different factors, including the G-box binding factor (GBF), GA-1, GC-1, AT-1, and GT-1, have been shown to bind to different promoter elements, probably mediating light responsiveness through protein-protein interactions (Schindler et al, 1990(Schindler et al, , 1992a(Schindler et al, , 1992cDehesh et al, 1992;Gilmartin et al, 1992;Perisic and Lam, 1992). A similar picture is found in the light-regulated element of the chs promoter (termed unit 1) of parsley and mustard.…”