Figure 2.

Superhelical density of endogenous 2-μ plasmid in various histone mutants. The labels at the top indicate various H4 mutations carried on plasmid B in combination with H3 Δ4–30. W.T., wild type. A small open circle on the left of each lane marks the center of distribution of topoisomers identified by densitometric tracing. G and D designate samples from cells grown in galactose and glucose, respectively. These experiments demonstrate that mutation of H4 K5/K12 has no apparent effect on superhelical density of plasmid in vivo. The greatest effect on superhelical density, a measure of nucleosome assembly, occurs when K5, K8, and K12 are mutated simultaneously.