What Parts of the Nucleosome Does NuA4 Bind To?

The DNA in the nuclei of eukaryotic cells is organized into a structure called chromatin. The basic unit of chromatin is the nucleosome, which contains DNA tightly wrapped around eight histone proteins, two each of histones H2A, H2B, H3, and H4. Chromatin prevents other proteins from accessing the DNA and must be disassembled before transcription can take place.The NuA4 lysine acetyltransferase (KAT) complex acetylates histones H4 and H2A, weakening the histone-DNA interactions, and stimulating chromatin disassembly. NuA4 is the only essential KAT in yeast and is involved in transcription, DNA repair, and cell cycle control. While NuA4 acetylates nucleosomes, it is largely unknown how NuA4 actually binds to the nucleosome. We investigated the parts of the nucleosome bound by NuA4 by screening a library of histone point mutants for defects in H4 acetylation. We have so far analyzed H2A and parts of H2B and H4. We found mutations in all three histones that increased and decreased H4 acetylation. As expected, mutation of NuA4 targets H4K5 and K8 dramatically reduced acetylation. H2A L66A reduced acetylation. The most surprising mutations affecting H4 acetylation were threonine 118 and serine 125 in H2B, which both reduced H4 acetylation. We will continue to confirm these results and examine how the mutations affect NuA4-nucleosome binding. Our preliminary finding suggests that NuA4 may be able to interact with multiple parts of the nucleosome