Genetic Reagents
A yeast strain (UKY403) in which the sole copy of histone H4 is under the control of the GAL1 promoter was previously constructed and used to examine the effects of depleting nucleosomes on expression of various genes (15-18). Growth in galactose media produces normal levels of histone H4 mRNA, but this is rapidly repressed upon addition of glucose, leading to a reduction of the nucleosomal content of yeast cells by 50% within six hours (16,17).
The Sir2p, Sir3p, Sir4p, and Rap1p proteins are thought to be required for telomeric silencing, with Sir3p playing a particularly important role (7-9,13). We identified genes whose expression and silencing is dependent on Sir2p, Sir3p, and Rap1p proteins using strains completely deleted for the genes encoding these proteins.