Analysis of the histone acetyltransferase B complex of maize embryos

Purified histone acetyltransferase B (HAT-B) from maize consists of two sub units, p50 and p45, Cloning of the cDNA and genomic DNA encoding the cataly tic subunit p50 revealed a consensus motif reminiscent of other acetyltrans ferases. Internal peptide sequences and-immunological studies identified p4 5 as a protein related to the Retinoblastoma associated protein Rbap. Antib odies against recombinant p50 were able to immunoprecipitate the enzymatic activity of p50 as well as p45. Consistent with the idea that HAT-B is invo lved in acetylation of newly synthesized histone H4 during DNA replication, mRNA and protein levels are correlated with S-phases during embryo germina tion. Inhibition of histone deacetylases by HC toxin or Trichostatin A caus ed a decrease of the in vivo expression of HAT-B mRNA, Regardless of its pr edominant cytoplasmic localization, a significant proportion of HAT-B-p50 i s present in nuclei, irrespective of the cell cycle stage, suggesting an ad ditional nuclear function.