HISTONE ACETYLATION - A POSSIBLE MECHANISM FOR THE INHERITANCE OF CELL MEMORY AT MITOSIS

Immunofluorescent labelling demonstrates that human metaphase chromoso mes contain hyperacetylated histone H4. With the exception of the inac tive X chromosome in female cells, where the bulk of histone H4 is und eracetylated, H4 hyperacetylation is non-uniformly distributed along t he chromosomes and clustered in cytologically resolvable chromatin dom ains that correspond, in general, with the R-bands of conventional sta ining. The strongest immunolabelling is often found in T-bands, the su bset of intense R-bands having the highest GC content. The majority of mapped genes also occurs in R-band regions, with the highest gene den sity in T-bands. These observations are consistent with a model in whi ch hyperacetylation of histone H4 marks the position of potentially ac tive gene sequences on metaphase chromosomes. Since acetylation is mai ntained during mitosis, progeny cells receive an imprint of the histon e H4 acetylation pattern that was present on the parental chromosomes before cell division. Histone acetylation could provide a mechanism fo r propagating cell memory, defined as the maintenance of committed sta tes of gene expression through cell lineages.