Lysine 4 on H3 and its adjacent residues are involved in HU-mediated response in a redundant manner with the H2A N-tail. (A) HU sensitivities of mutant strains carrying tailless H2A (tH2A) and truncated H3 (tH3d5: H3Δ1–5). (B) HU sensitivities of mutants carrying tH2A and a point mutation on H3 (H3S1A, H3R2A, H3T3A, H3K4A, H3Q5A). (C) HU sensitivities of set1 deletion mutant cells combined with histone mutations (tH2A, tH3K4A, or tH2A:tH3K4A). (D) Exponentially growing histone mutant, tH2A:H3K4A, H3K4A, and wild-type cells (labeled as WT) were treated with 100 mM HU or 0.2% MMS for 2 h. Whole-cell extracts from the mutant cells were subjected to immunoblot analyses with indicated antibodies against Rad53, H2AS129ph (labeled as S129ph), and H2A.