Mutations in both the structured domain and N-terminus of histone H2B bypass the requirement for Swi-Snf in yeast.

The chromatin elements targeted by the ATPdependent, Swi–Snf nucleosome‐remodeling complex are unknown. To address this question, we generated mutations in yeast histone H2B that suppress phenotypes associated with the absence of Swi–Snf. Sin − (Swi–Snf‐independent) mutations occur in residues involved in H2A–H2B dimer formation, dimer–tetramer association, and in the H2B N‐terminus. The strongest and most pleiotropic Sin − mutation removed 20 amino acid residues from the H2B N‐terminus. This mutation allowed active chromatin to be formed at the SUC2 locus in a snf5Δ mutant and resulted in hyperactivated levels of SUC2 mRNA under inducing conditions. Thus, the H2B N‐terminus may be an important target of Swi–Snf in vivo . The GCN5 gene product, the catalytic subunit of several nuclear histone acetytransferase complexes that modify histone N‐termini, was also found to act in conjunction with Swi–Snf. The phenotypes of double gcn5Δsnf5Δ mutants suggest that histone acetylation may play both positive and negative roles in the activity of the Swi–Snf‐remodeling factor.