The upstream regulatory region of daf - 7 contains a conserved HSF - 1 binding site that is responsive in vivo. A, The structure of daf-7; purple boxes represent exonic sequences; grey boxes indicate upstream and downstream regulatory sequences. The position of this conserved HSF-1 binding site is indicated by the red arrow. B, This site is highly conserved in the daf-7 genomic environment of Caenorhabditis species. Red letters indicate strictly conserved sequences within the consensus HSF-1 binding site. C, Scheme of a transcriptional fusion gfp-labeled daf-7 reporter (pdaf-7::gfp) driven by a 3.8 kb long upstream regulatory sequence. A mutated version of the reporter (pmutdaf-7::gfp) lacking several nucleotides from the potential HSF-1 binding site (grey letters in the next upper panel) is also shown. D, The daf-11(m47) mutation strongly represses the expression of the wild-type reporter (the repression occurs with full penetrance). The promoter-mutated construct, however, is not responsive to the daf-11(m47) mutation: m47 fails to downregulate pmutdaf-7::gfp. 82% of these transgenic daf-11(m47) animals showed strong (wild-type levels) daf-7 expression (N=264). This suggests an in vivo functionality for this particular HSF-1-binding element.