The assembly of regularly spaced nucleosomes in the Xenopus oocyte S-150 extract is accompanied by deacetylation of histone H4.

Histone proteins, which were assembled into chromatin using the Xenopus oocyte S-150 extract, were analyzed on acid-urea gels and Triton-acid-urea gels to determine their state of modification. We find that histone H4, which is present in a diacetylated form in the oocyte S-150, gradually loses its acetate groups as the DNA is packaged into chromatin. Thus, this process parallels the one observed in vivo during chromatin formation in growing eucaryotic cells. Histone H4 deacetylation in the oocyte S-150 is a DNA-dependent reaction. This reaction is blocked when butyrate (an inhibitor of histone deacetylase) is added at the onset of the chromatin assembly process. When butyrate is added at the end of the assembly process, no de novo acetylation of the nucleosomal histone H4 is observed. Chromatin with regularly spaced nucleosomes, displaying periodicities ranging from 160 to 220 base pairs, can be assembled in vitro with the oocyte S-150 (Rodríguez-Campos, A., Shimamura, A., and Worcel, A. (1989) J. Mol. Biol., in press). This chromatin may contain either deacetylated histone H4 when assembled under standard conditions or diacetylated H4 when assembled in the presence of butyrate. Both types of chromatin display identical structures upon digestion with nucleases. The potential applications of this system toward the study of the naturally occurring diacetylated histone H4 are discussed.