A tandem array containing 12 copies of a histone gene repeat unit. The His3 gene in each copy of the repeat has been mutated to carry amino acid substitutions K4R and K27R.

Wild-type His1 gene in the context of a histone gene repeat tandem array.

Wild-type His2A gene in the context of a histone gene repeat tandem array. Two silent mutations have been introduced into the His2A coding sequence, which removes an XhoI restriction site.

Wild-type His2B gene in the context of a histone gene repeat tandem array.

Mutant His3 gene (amino acid replacements K4R and K27R) in the context of a histone gene repeat tandem array.

Wild-type His4 gene in the context of a histone gene repeat tandem array.