GATA transcription factors are a group of DNA binding proteins broadly distributed in eukaryotes. The GATA factors DNA binding domain is a class IV zinc finger motif in the form CX 2 CX 17-20 CX 2 C followed by a basic region. In plants, GATA DNA motifs have been implicated in light-dependent and nitrate-dependent control of transcription. Herein, we show that the Arabidopsis and the rice (Oryza sativa) genomes present 29 and 28 loci, respectively, that encode for putative GATA factors. A phylogenetic analysis of the 57 GATA factors encoding genes, as well as the study of their intron-exon structure, indicates the existence of seven subfamilies of GATA genes. Some of these subfamilies are represented in both species but others are exclusive for one of them. In addition to the GATA zinc finger motif, polypeptides of the different subfamilies are characterized by the presence of additional domains such as an acidic domain, a CCT (CONSTANS, CO-like, and TOC1) domain, or a transposase-like domain also found in FAR1 and FHY3. Subfamily VI comprises genes that encode putative bi-zinc finger polypeptides, also found in metazoan and fungi, and a tri-zinc finger protein which has not been previously reported in eukaryotes. The phylogeny of the GATA zinc finger motif, excluding flanking regions, evidenced the existence of four classes of GATA zinc fingers, three of them containing 18 residues in the zinc finger loop and one containing a 20-residue loop. Our results support multiple models of evolution of the GATA gene family in plants including gene duplication and exon shuffling.GATA factors are a class of transcriptional regulators present in fungi, metazoans, and plants that normally recognize the consensus sequence WGATAR (W ¼ T or A; R ¼ G or A; Lowry and Atchley, 2000). The DNA binding domain of GATA factors is constituted by a type IV zinc finger in the form CX 2 CX 17-20 CX 2 C followed by a highly basic region. In animals, where GATA factors have been shown to play critical roles in development, differentiation, and control of cell proliferation, the GATA DNA binding domain adopts the form CX 2 CX 17 CX 2 C (Patient and McGhee, 2002). Vertebrate and many invertebrate GATA proteins present two of these zinc fingers, where only the C-terminal finger (C-finger) is involved in DNA binding. The N-terminal zinc finger (N-finger) can modulate the binding of the C-finger to specific GATA sites (Trainor et al., 2000), bind DNA with different specificity (Pedone et al., 1997;Newton et al., 2001), or mediate the interaction with transcription cofactors of the Friend of GATA (FOG) family (Tsang et al., 1997;Fox et al., 1998). The majority of the fungal GATA factors contain a single zinc finger domain and mostly fall into two different categories: those with 17-residue loops (CX 2 CX 17 CX 2 C; also called zinc finger type IVa) and those with 18-residue loops (CX 2 CX 18 CX 2 C; also called zinc finger type IVb; Teakle and Gilmartin, 1998). Nineteen-and 20-residue zinc finger loops are also found, albeit rarely, in fungi. For...
In cyanobacteria, after transport by specific permeases, ammonium is incorporated into carbon skeletons by the sequential action of glutamine synthetase (GS) and glutamate synthase (GOGAT). Two types of GS (GSI and GSIII) and two types of GOGAT (ferredoxin-GOGAT and NADH-GOGAT) have been characterized in cyanobacteria. The carbon skeleton substrate of the GS-GOGAT pathway is 2-oxoglutarate that is synthesized by the isocitrate dehydrogenase (IDH). In order to maintain the C-N balance and the amino acid pools homeostasis, ammonium assimilation is tightly regulated. The key regulatory point is the GS, which is controlled at transcriptional and posttranscriptional levels. The transcription factor NtcA plays a critical role regulating the expression of the GS and the IDH encoding genes. In the unicellular cyanobacterium Synechocystis sp. PCC 6803, NtcA controls also the expression of two small proteins (IF7 and IF17) that inhibit the activity of GS by direct protein-protein interaction. Cyanobacteria perceive nitrogen status by sensing the intracellular concentration of 2-oxoglutarate, a signaling metabolite that is able to modulate allosterically the function of NtcA, in vitro. In vivo, a functional dependence between NtcA and the signal transduction protein PII in controlling NtcA-dependent genes has been also shown.
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