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. 1997 Apr 1;94(7):2885–2890. doi: 10.1073/pnas.94.7.2885

Figure 1.

Figure 1

Repression of histone H4 gene results in nucleosome depletion over the MMTV promoter. (A) Schematic representation of histone H4-mediated nucleosome depletion, according to the method developed by Grunstein and collaborators (26). (B) Superhelicity of episomes carrying the MMTV–lacZ reporter in SChY50 cells grown in galactose- or glucose-containing media (17). The modal value of the distribution of topoisomers is indicated by arrows. The difference between cells grown in galactose (Gal) and in glucose (Glu) corresponds to 40% nucleosome depletion. Superhelicity analysis was performed as described (32) but hybridizing with an Escherichia coli lacZ probe. (C) Micrococcal nuclease (MNase) sensitivity of MMTV promoter in normal (galactose) or histone H4-depleted chromatin (glucose) of SChY50 cells (17). Note that in glucose medium the nuclease digestion is more effective and leads to appearance of shorter polynucleosomes and mononucleosomes. MMTV sensitivity to micrococcal nuclease was assayed as described (17) with a probe extending from −173 to −78 in the MMTV promoter.