Dancing the cell cycle two-step: regulation of yeast G1-cell-cycle genes by chromatin structure

• The yeast HO and CLN2 genes are both activated by the SBF factor and expressed in the G1 phase of the cell cycle.
• Activation of HO requires multiple activators to sequentially evict nucleosomes from distinct promoter regions in a multi-step promoter.
• The CLN2 promoter has SBF binding sites in a nucleosome-depleted region, ensuring reliable expression in each cell cycle.
• The transcriptional regulation of these two genes illuminates how chromatin structure can define regulatory properties of promoters.

The chromatin structure at a promoter can define how a gene is regulated. Studies of two yeast genes expressed in the G1 phase of the cell cycle, HO and CLN2, have provided important paradigms for transcriptional regulation. Although the SBF (Swi4/Swi6 box factor) transcription factor activates both genes, the chromatin landscapes that regulate SBF binding are different. Specifically, the CLN2 promoter is constitutively available for SBF binding, whereas HO has a complex two-step promoter in which chromatin changes in one region allow SBF to bind at a downstream location. These studies reveal the role of chromatin in defining the regulatory properties of promoters.