FIG. 5.

HMRa chromatin near the E silencer. Chromatin structure was mapped by primer extension analysis of micrococcal nuclease cleavage sites. Wild-type (WT) and sir3 mutant strains are indicated. Triangles represent increasing concentrations of nuclease. Lane O, a nuclease-free control; lane D, protein-free DNA subjected to nuclease cleavage. The inferred positions of nucleosomes R9 to R12 are indicated. Four precisely positioned nucleosomes are located adjacent to the I silencer. Their structure in the sir3 mutants was disrupted, evidenced by the widespread nuclease accessibility.