Histone chaperone Rtt106 promotes nucleosome formation using (H3-H4) ₂ tetramers

The yeast histone chaperone Rtt106 is involved in de novo assembly of newly synthesized histones into nucleosomes during DNA replication and plays a role in regulating heterochromatin silencing and maintaining genomic integrity. The interaction of Rtt106 with H3-H4 is modulated by acetylation of H3 lysine 56 catalyzed by the lysine acetyltransferase Rtt109. Using affinity purification strategies, we demonstrate that Rtt106 interacts with (H3-H4)₂ heterotetramers in vivo. In addition, we show that Rtt106 undergoes homo-oligomerization in vivo and in vitro, and mutations in the N-terminal homodimeric domain of Rtt106 that affect formation of Rtt106 oligomers compromise the function of Rtt106 in transcriptional silencing and response to genotoxic stress and the ability of Rtt106 to bind (H3-H4)₂. These results indicate that Rtt106 deposits H3-H4 heterotetramers onto DNA and provide the first description of a H3-H4 chaperone binding to (H3-H4)2 heterotetramers in vivo.