Two types of heat shock factors in cultured tobacco cells

We have isolated two types of complementary DNA (cDNA) sequences showing high similarity with the DNA-binding domain in heat shock factors (HSFs) from a cDNA library of tobacco suspension-cultured cells (Nicotiana tabacum L. cv. BY2). These two genes, NtHSF1 and NtHSF2, showed low similarity (37%) with each other. Both contained the typical conserved regions of HSFs (DNA-binding domains, leucine zipper repeats, nuclear localization signals, and tryptophan repeats). Transcripts of NtHSF1 and NtHSF2 were detected even at the normal temperature. The recombinant NtHSF1 and NtHSF2 proteins expressed in Escherichia coli bound specifically to a 183-bp DNA fragment of the Arabidopsis thaliana HSP18.2 promoter containing three sets of head-to-head and tail-to-tail repeats of the conserved pentamer unit (nGAAnnTTCnnGAAn).