Reduced Gene Dosage of Histone H4 Prevents CENP-A Mislocalization in Budding Yeast

Mislocalization of the centromeric histone H3 variant (Cse4 in budding yeast, CID in flies, CENP-A in humans) contributes to chromosomal instability (CIN) in yeast, fly, and human cells. Overexpression and mislocalization of CENP-A has been observed in several cancers. However, the mechanisms that contribute to the mislocalization of CENP-A are not fully understood. In this study, we used budding yeast to identify genes that facilitate the mislocalization of Cse4 to non-centromeric regions. Previous studies have shown that E3 ligases (Psh1, Slx5, Cdc4) and factors such as Doa1, Hir2, and Cdc7 regulate proteolysis of Cse4 and prevent its mislocalization. Overexpressed Cse4 (GALCSE4) is highly stable and causes synthetic dosage lethality (SDL) in psh1Δ, slx5Δ, doa1Δ, hir2Δ, cdc4-1, and cdc7-4 strains. We used a genome-wide screen to identify suppressors of the psh1Δ GALCSE4 SDL. Deletions of histone H4 alleles (HHF1 or HHF2) were among the top suppressors of psh1Δ GALCSE4 SDL. Here we show that reduced gene dosage of H4 prevents mislocalization of Cse4 and promotes faster degradation of Cse4 in a psh1Δ GALCSE4 strain. Deletion of either HHF1 or HHF2 also suppresses the GALCSE4 SDL in slx5Δ, doa1Δ, hir2Δ, cdc4-1, and cdc7-4 strains. Suppression of psh1Δ GALCSE4 SDL by hhf1-20, which is defective for interaction with Cse4, suggests that defects in the Cse4-H4 interaction prevents mislocalization of Cse4. In summary, our genome-wide screen identified genes that contribute to Cse4 mislocalization and we show how reduced dosage of histone H4-encoding genes prevents mislocalization of Cse4 into non-centromeric regions.