Arabidopsis heat shock factor: isolation and characterization of the gene and the recombinant protein.

We have isolated the Arabidopsis heat shock factor gene Athsf1 as genomic and corresponding cDNA sequences via cross-hybridization with tomato clones. Sequence analysis indicates only a partial homology with the HSFs from tomato and other organisms which is confined to the DNA-binding and the oligomerization domains. The gene is constitutively expressed but the level of mRNA for Athsf1 increases two-fold upon heat shock. However, the putative promoter region lacks the canonical heat shock elements. After expression in Escherichia coli the recombinant Athsf1 protein binds specifically to a synthetic oligonucleotide containing five heat shock elements. The native size of recombinant ATHSF1 in vitro is consistent with a trimer as demonstrated by chemical cross-linking and pore exclusion limit analysis.