DNA-BINDING FACTOR GT-2 FROM ARABIDOPSIS

Complementary DNA clones encoding a DNA-binding factor have been obtai ned from Arabidopsis by DNA hybridization with a GT-2 factor cDNA clon e from rice. The GT-2 gene appears to be present as a single copy in t he Arabidopsis genome and is transcribed as a 2.1 kb mRNA which is not light-regulated. The longest open reading frame in the sequenced clon es predicts a protein of 65 kDa, beginning with the first in-frame met hionine. The protein contains basic, acidic, and proline/glutamine-ric h motifs and has significant amino acid sequence homology to the rice GT-2 factor, including three regions of 50-75 amino acids each of grea ter than 60% identity. Two of these regions are predicted to form simi lar trihelix structures postulated to be involved in selective binding to specific variations of a GT-box motif DNA sequence found in the pr omoter regions of several plant genes. Except for weak similarity to a tobacco GT-box binding factor, GT-1a/B2F, Arabidopsis GT-2 has no sim ilarity to other sequences in the databases. DNA-binding studies show that Arabidopsis GT-2 has binding characteristics similar to those of the rice GT-2 factor, but dissimilar to those of the tobacco GT- 1 a/B 2F factor. The data indicate that a DNA-binding factor containing doma ins of similar structure and target-sequence specificity has been cons erved between monocots and dicots.