ARABIDOPSIS-THALIANA CBF1 ENCODES AN AP2 DOMAIN-CONTAINING TRANSCRIPTIONAL ACTIVATOR THAT BINDS TO THE C-REPEAT DRE, A CIS-ACTING DNA REGULATORY ELEMENT THAT STIMULATES TRANSCRIPTION IN RESPONSE TO LOW-TEMPERATURE AND WATER-DEFICIT/

Recent efforts have defined a cis-acting DNA regulatory element in pla nts, the C-repeat/dehydration responsive element (DRE), that stimulate s transcription in response to low temperature and water deficit, Here we report the isolation of an Arabidopsis thaliana cDNA that encodes a C-repeat/DRE binding factor, CBF1 (C-repeat/DRE Binding Factor 1), A nalysis of the deduced CBF1 amino acid sequence indicates that the pro tein has a molecular mass of 24 kDa, a potential nuclear localization sequence, and a possible acidic activation domain, CBF1 also has an AP 2 domain, which is a DNA-binding motif of about 60 aa present in the A rabidopsis proteins APETALA2, AINTEGUMENTA, and TINY; the tobacco ethy lene response element binding proteins; and numerous other plant prote ins of unknown function, The transcript levels for CBF1, which appears to be a single or low copy number gene, did not change appreciably in plants exposed to low temperature or in detached leaves subjected to water deficit, Binding of CBF1 to the C-repeat/DRE was demonstrated in gel shift assays using recombinant CBF1 protein expressed in Escheric hia coli. Moreover, expression of CBF1 in yeast aas found to activate transcription of reporter genes containing the C-repeat/DRE as an upst ream activator sequence but not mutant versions of the DNA element, We conclude that CBF1 can function as a transcriptional activator that b inds to the C-repeat/DRE DNA regulatory element and, thus, is likely t o have a role in cold- and dehydration-regulated gene expression in Ar abidopsis.