FIG. 5.

Interconversion of ac and m8 promoter responses to NICD upon mutation of their S-site architectures. (A) The single endogenous S site in the wild-type ac promoter (ac-WT) did not mediate depression or activation when NICD was coexpressed with the Ac/Da bHLH A proteins (experiments 1 to 4). In contrast, when a second S site is added to the ac promoter so that an SPS element is created (ac-SPS), coexpression of NICD and Ac/Da synergistically activated reporter gene transcription very strongly (experiments 5 to 8). (B) The wild-type m8 promoter, which contains an SPS element, mediates synergistic activation of reporter gene expression when NICD and Ac/Da are coexpressed (experiments 9 to 12). In contrast, NICD and Ac/Da proteins do not synergistically activate a modified m8 promoter (m8-mut) with one of the S sites in the SPS element mutated so that the remaining single S site is in the same orientation as the wild-type ac promoter (experiments 13 to 16). Together, these findings with ac and m8 demonstrate the functional importance of S-site architecture in mediating differential transcriptional responses to Notch signaling. The arrows indicate the S binding site orientation.