RESUMO
Purified histone acetyltransferase B (HAT-B) from maize consists of two subunits, p50 and p45. Cloning of the cDNA and genomic DNA encoding the catalytic subunit p50 revealed a consensus motif reminiscent of other acetyltransferases. Internal peptide sequences and immunological studies identified p45 as a protein related to the Retinoblastoma associated protein Rbap. Antibodies against recombinant p50 were able to immunoprecipitate the enzymatic activity of p50 as well as p45. Consistent with the idea that HAT-B is involved in acetylation of newly synthesized histone H4 during DNA replication, mRNA and protein levels are correlated with S-phases during embryo germination. Inhibition of histone deacetylases by HC toxin or Trichostatin A caused a decrease of the in vivo expression of HAT-B mRNA. Regardless of its predominant cytoplasmic localization, a significant proportion of HAT-B-p50 is present in nuclei, irrespective of the cell cycle stage, suggesting an additional nuclear function.
