A novel class of plant-specific zinc-dependent DNA-binding protein that binds to A/T-rich DNA sequences

Complementary DNA encoding. a DNA-binding protein, designated PLATZ1 (plant AT-rich sequence-and zinc-binding protein 1), was isolated from peas. The amino acid sequence of the protein is similar to those of other uncharacter ized proteins predicted from the genome sequences of higher plants. However , no paralogous sequences have been found outside the plant kingdom. Multip le alignments among these paralogous proteins show that several cysteine an d histidine residues are invariant, suggesting that these proteins are a no vel class of zinc-dependent DNA-binding proteins with two distantly located regions, C-x(2)-H-x(11)-C-x(2-)C-x((4-5))-C- x(2)-C-x((3-7))-H-x(2)-H and C-x(2)-C-x((10-11))-C-x(3)-C. In an electrophoretic mobility shift assay, t he zinc chelator 1,10-o-phenanthroline inhibited DNA binding, and two dista nt zinc-binding regions were required for DNA binding. A protein blot with (ZnCl2)-Zn-65 showed that both regions are required for zinc-binding activi ty. The PLATZ1 protein non-specifically binds to A/T-rich sequences, includ ing the upstream region of the pea GTPase pra2 and plastocyanin petE genes. Expression of the PLATZ1 repressed those of the reporter constructs contai ning the coding sequence of luciferase gene driven by the cauliflower mosai c virus (CaMV) 35S90 promoter fused to the tandem repeat of the A/T-rich se quences. These results indicate that PLATZ1 is a novel class of plant-speci fic zinc-dependent DNA-binding protein responsible for A/T-rich sequence-me diated transcriptional repression.