Heterodimerization between light-regulated and ubiquitously expressed Arabidopsis GBF bZIP proteins.

Abstract

The promoters of a variety of plant genes are characterized by the presence of a G‐box (CCACGTGG) or closely related DNA motifs. These genes often exhibit quite diverse expression characteristics and in many cases the G‐box sequence has been demonstrated to be essential for expression. The G‐box of the Arabidopsis rbcS‐1A gene is bound by a protein, GBF, identified in plant nuclear extracts. Here we report the isolation of three Arabidopsis thaliana cDNA clones encoding GBF proteins referred to as GBF1, GBF2 and GBF3. GBF1 and GBF2 mRNA is present in light and dark grown leaves as well as in roots. In contrast, GBF3 mRNA is found mainly in dark grown leaves and in roots. The deduced amino acid sequences of the three cDNAs indicate that each encodes a basic/leucine zipper protein. In addition, all three proteins are characterized by an N‐terminal proline‐rich domain. Homodimers of the three proteins specifically recognize the G‐box motif, with GBF1 and GBF3 binding symmetrically to this palindromic sequence. In contrast, GBF2 binds to the symmetrical G‐box sequence in such a way that the juxtaposition of the protein and the DNA element is clearly asymmetric and hence distinct from that observed for the other two proteins. The fact that GBF1, GBF2 and GBF3 possess both distinct DNA binding properties and expression characteristics prompt us to entertain the notion that these proteins may individually mediate distinct subclasses of expression properties assigned to the G‐box. Furthermore, we demonstrate that GBF1, GBF2 and GBF3 heterodimerize and these heterodimers also interact with the G‐box, suggesting a potential mechanism for generating additional diversity from these GBF proteins.

Two bZIP proteins from Antirrhinum flowers preferentially bind a hybrid C‐box/G‐box motif and help to define a new sub‐family of bZIP transcription factors

“…For the Antirrhinum bZIPs, the random binding site selection suggested that the hybrid C-box/G-box element, found in many plant gene promoters, is their preferred target. The selection of this site by bZIP910 and bZIP911 was more clear-cut than in random binding site selection studies for other plant bZIP proteins (Niu and Guiltinan, 1994;Schindler et al, 1992c), suggesting that bZIP910 and bZIP911 have relatively sharply defined target motifs. The consequent result of a FINDPATTERNS search (Devereux et al, 1984) suggested that the role of these bZIPs could be to regulate the expression of histone genes and/or a subset of chloroplastic genes encoded in the nucleus.…”

“…bZIP910, bZIP911, OBF1, MLIP15 (LIP15), LIP19, At7568 (AT7568) and At1507 (AT1507) form a sub-family more closely related to each other in sequence composition of their bZIP domains than to other bZIP proteins. Other bZIP proteins included are CPRF-1, 2 and 3 (Weisshaar et al, 1991) from parsley; TGA1b (Katagiri et al, 1989) from tobacco, GBF1 (Schindler et al, 1992c) from Arabidopsis, GBF9G, (Meier and Gruissem, 1994) from tomato, HBP1a and HBPlac14 (Mikami et al, 1994;Tabata et al, 1989) from wheat, and OHP1 and O2 (Hartings et al, 1989;Pysh et al, 1993) from maize.…”

Characterization of a maize G‐box binding factor that is induced by hypoxia

“…This bipartite structure is characteristic of the bZlP class of DNA binding proteins (Vinson et aL, 1989). To date, 11 cDNAs GBFs have been isolated from five different plant species, all of them are bZlP proteins (Guiltinan et aL, 1990;Meier and Gruissem, 1994;Oeda et aL, 1991;Schindler et aL, 1992a;Tabata et aL, 1989;Weisshaar et al, 1991). Amino acid sequence comparison Maize GBF induced by hypoxia 597 of the plant GBFs shows a high degree of conservation (85% or more identical residues) in the basic domain, the amino acids that are thought to come in contact with the DNA.…”

Intracellular localization of GBF proteins and blue light‐induced import of GBF2 fusion proteins into the nucleus of cultured Arabidopsis and soybean cells

“…GBF4 contains an acidic putative activation motif (Menkens and Cashmore, 1994). All these GBFs except GBF4 can homodimerize, and, except for the GBF1/ GBF4 combination, all four can freely heterodimerize with one another to form various functional DNA-binding complexes with potentially distinct binding affinities and activation abilities (Menkens and Cashmore, 1994;Schindler et al, 1992a).…”