Maternal histone deacetylase is accumulated in the nuclei of Xenopus oocytes as protein complexes with potential enzyme activity

Reversible acetylation of core histones plays an important regulatory role in transcription and replication of chromatin, The acetylation status of ch romatin is determined by the equilibrium between activities of histone acet yltransferases (HATs) and histone deacetylases (HDACs), The Xenopus protein HDACm shows sequence homology to other putative histone deacetylases, but its mRNA is expressed only during early development, Both HDACm protein and acetylated non-chromosomal histones are accumulated in developing oocytes, indicating that the key components for histone deposition into new chromat in during blastula formation are in place by the end of oogenesis. Here we show that the 57 kDa HDACm protein undergoes steady accumulation in the nuc leus, where it is organized in a multiprotein complex of approx. 300 kDa, A second, major component of the nuclear complex is the retinoblastoma-assoc iated protein p48 (RbAp48/46), which may be used as an adaptor to contact a cetylated histones in newly assembled chromatin, The nuclear complex has HD AC activity that is sensitive to trichostatin A, zinc ions and phosphatase treatment. The 57 kDa protein serves as a marker for total HDAC activity th roughout oogenesis and early embryogenesis, The active HDACm complex and it s acetylated histone substrates appear to be kept apart until after chromat in assembly has taken place. However, recombinant HDACm, injected into the cytoplasm of oocytes, not only is translocated to the nucleus, but also is free to interact with the endogenous chromatin.