GAL4 directs nucleosome sliding induced by NURF

The Drosophila nucleosome remodeling factor (NURF) is an imitation switch (ISWI)-containing chromatin remodeling complex that can catalyze nucleosome repositioning at promoter regions to regulate access by the transcription machinery. Mononucleosomes reconstituted in vitro by salt dialysis adopt an ensemble of translational positions on DNA templates. NURF induces bi-directional ‘sliding’ of these nucleosomes to a subset of preferred positions. Here we show that mononucleosome sliding catalyzed by NURF bears similarity to nucleosome movement induced by elevated temperature. Moreover, we demonstrate that the GAL4 DNA-binding domain can extend NURF-induced nucleosome movement on a GAL4-E4 promoter, expanding the stretch of histone-free DNA at GAL4 recognition sites. The direction of NURF-induced nucleosome movement can be significantly modulated by asymmetric placement of tandem GAL4 sites relative to the nucleosome core particle. As such, sequence-specific, transcription factor-directed nucleosome sliding is likely to have substantial influence on promoter activation.