Stable nucleosome positioning and complete repression by the yeast α2 repressor are disrupted by amino-terminal mutations in histone H4

Nucleosomes are positioned in the presence of the yeast repressor α2 in minichromosomes containing the α2 operator and on the promoters of a-cell-specific genes regulated by α2. To investigate the possibility that α2 directs nucleosome position through an interaction with a component of the core particle, we analyzed chromatin structures adjacent to the operator in a cells containing mutations in the amino-terminal region of histone H4. Deletion or point mutation of specific amino acids in histone H4 altered the location and/or stability of nucleosomes adjacent to the α2 operator. These changes in chromatin structure were accompanied by partial derepression of a β-galactosidase reporter construct under α2 control, even though α2 remained bound to its operator sequence. Our data suggest that complete repression by α2 requires stable positioning of nucleosomes in promoter regions and this positioning involves the conserved amino-terminal region of histone H4.