Single nucleosome ChIPs identify an extensive switch of acetyl marks on cell cycle promoters.

Histones are modified by different post-translational modifications which are marks of peculiar chromatin functions. We previously evaluated histone methylations of G1/S and G2/M cell-cycle promoters at the single nucleosome level; here we report an analysis of acetylation marks, including some for which essentially nothing is known. In general, our data confirm the presence of H3/H4, but not H2A/H2B, in active core promoters. H3K14ac and H3K27ac are associated with active promoters, while H3K9ac and H3K18ac are more ambiguous, being also found under repression. Acetylation of H3K36, H3K79 and H2BK120, all residues involved in positive function through methylations or monoubiquitination, were found on repressed genes. H2Bub was present only on transcribed areas, and absent on core promoters or upstream nucleosomes. KAT2A/KAT2B and subunits of the SAGA and ATAC complexes have differential and dynamic roles: KAT2A-inactivated MEFs show a G1/S block, and KAT2B is important for G2/M. Furthermore, the precision of our analysis allows us to locate some acetylations specifically occurring upstream, downstream or in core promoters. Overall, the switch between methylations-and monoubiquitination-and acetylations on histone Lysines is a general theme on this dynamic group of genes.