Highly efficient chromatin transcription induced by superhelically curved DNA segments: The underlying mechanism revealed by a yeast system

Superhelically curved DNA. structures can strongly activate transcription in mammalian cells. However, the mechanism underlying the activation has not been clarified. We investigated this mechanism in yeast cells, using 108,180, and 252 bp synthetic curved. DNA segments. Even in the presence of nucleosomes, these DNAs activated transcription from a UAS-deleted CYC1 promoter that is silenced in the presence of nucleosomes. The fold-activations of transcription by these segments, relative to the transcription on the control that lacked such segments, were 51.4, 63.4, and 56.4, respectively. The superhelically curved DNA structures favored, nucleosome formation. However, the translational positions of the nucleosomes were dynamic. The high mobility of the nucleosomes on the superhelically curved DNA structures seemed to influence the mobility of the nucleosomes formed on the promoter and eventually enhanced the access to the center region of one TATA sequence. Functioning as a dock for the histone core and allowing nucleosome sliding seem to be the mechanisms underlying the transcriptional activation by superhelically curved DNA structures in chromatin. The present study provides important clues for designing and constructing artificial chromatin modulators, as a tool for chromatin engineering.