CHROMOSOMAL MAPPING OF CORE HISTONE ACETYLATION BY IMMUNOSELECTION

Acetylation of specific lysine residues in the N-terminal domains of c ore histones is a biochemical marker of active genes. To determine the spatial and temporal distribution of this reversible posttranslationa l modification, affinity-purified polyclonal antibodies recognizing th e epitope epsilon-acetyllysine have been used in immunoselection proce dures with mononucleosomes and salt-soluble chromatin fragments genera ted by micrococcal nuclease. The DNA of the antibody-selected chromati n was slot-blotted and probed with a variety of gene sequences: an enh anced hybridization signal, with respect to that from the DNA of the i nput chromatin, demonstrated elevated acetylation levels on the histon es associated with the probing sequences. Using chicken embryonic eryt hrocytes as chromatin source and probes from the beta globin locus, it was shown that both the embryonic epsilon and adult beta genes are ac etylated at 5 and 15 days, and the acetylation uniformly covers the wh ole of the locus, precisely comapping with the 33 kb of open chromatin structure. Studies with proliferating human K562 cells show that the inactive but poised PDGF-beta gene is already hyperacetylated and that its acetylation status is not enhanced on induction. These results in dicate that acetylation is not a consequence of transcription but a pr erequisite and that it may be responsible for either generating or mai ntaining the open structure of poised and active genes. (C) 1997 Acade mic Press.