PERSISTENT INTERACTIONS OF CORE HISTONE TAILS WITH NUCLEOSOMAL DNA FOLLOWING ACETYLATION AND TRANSCRIPTION FACTOR-BINDING

In this study, we examined the effect of acetylation of the NH, tail o f core histones on their binding to nucleosomal DNA in the absence or presence of bound transcription factors. To do this, we used a novel U V laser-induced protein-DNA cross-linking technique, combined with imm unochemical and molecular biology approaches. Nucleosomes containing o ne or five GAL4 binding sites were reconstituted with hypoacetylated o r hyperacetylated core histones. Within these reconstituted particles, UV laser-induced histone-DNA crosslinking was found to occur only via the nonstructured histone tails and thus presented a unique tool for studying histone tail interactions with nucleosomal DNA. Importantly, these studies demonstrated that the NH, tails were not released from n ucleosomal DNA upon histone acetylation, although some weakening of th eir interactions was observed at elevated ionic strengths. Moreover, t he binding of up to five GALA-AH dimers to nucleosomes occupying the c entral 90 bp occurred without displacement of the histone NH, tails fr om DNA. GALA-AH binding perturbed the interaction of each histone tail with nucleosomal DNA to different degrees, However, in all cases, gre ater than 50% of the interactions between the histone tails and DNA wa s retained upon GALA-AH binding, even if the tails were highly acetyla ted. These data illustrate an interaction of acetylated or nonacetylat ed histone tails with DNA that persists in the presence of simultaneou sly bound transcription factors.