Transcriptional adaptor and histone acetyltransferase proteins in Arabidopsis and their interactions with CBF1, a transcriptional activator involved in cold-regulated gene expression

The Arabidopsis CBF transcriptional activators bind to the CRT/DRE regulato ry element present in the promoters of many cold-regulated genes and stimul ate their transcription. Expression of the CBF1 proteins in yeast activates reporter genes carrying a minimal promoter with the CRT/DRE as an upstream regulatory element, Here we report that this ability of CBF1 is dependent upon the activities of three key components of the yeast Ada and SAGA compl exes, namely the histone acetyltransferase (HAT) Gcn5 and the transcription al adaptor proteins Ada2 and Ada3, This result suggested that CBF1 might fu nction through the action of similar complexes in Arabidopsis, In support o f this hypothesis we found that Arabidopsis has a homolog of the GCN5 gene and two homologs of ADA2, the first report of multiple ADA2 genes in an org anism, The Arabidopsis GCN5 protein has intrinsic HAT activity and can phys ically interact in vitro with both the Arabidopsis ADA2a and ADA2b proteins . In addition, the CBF1 transcriptional activator can interact with the Ara bidopsis GCN5 and ADA2 proteins, We conclude that Arabidopsis encodes HAT-c ontaining adaptor complexes that are related to the Ada and SAGA complexes of yeast and propose that the CBF1 transcriptional activator functions thro ugh the action of one or more of these complexes.