FIG. 2.

(A) Plasmid shuffle experiment of mutant histones to determine their viability. Strains expressing aberrant histones in the presence of wild-type proteins were plated with an initial OD₆₀₀ of 0.5 and serially diluted fivefold on both SC-Trp-Lys and on plates containing α-amino-adipate, which selects against the wild-type histone gene present on the LYS2 “shuffle” plasmid. As a negative control, the JPY12 yeast strain was transformed with a plasmid from which either histone H3 or H4 was completely deleted. (B) Southern blot analysis to determine whether cells expressing the mutated histones were compensating for their presence by increasing the copy number of the plasmid harboring the altered histone. Genomic DNA was extracted from each strain and probed for ACT1, a single-copy gene, and the plasmid backbone in a Southern blot analysis. The ratio of these band intensities was then compared with that of cells containing wild-type histones.