Abstract
Histones and transcription factors are regulated by a number of post-translational modifications that in turn regulate the transcriptional activity of genes. These modifications occur in large, multisubunit complexes. We have reported previously that mSin3A can recruit O-GlcNAc transferase (OGT) along with histone deacetylase into such a corepressor complex. This physical association allows OGT to act cooperatively with histone deacetylation in gene repression by catalyzing the O-GlcNAc modification on specific transcription factors to inhibit their activity. For rapid, reversible gene regulation, the enzymes responsible for the converse reactions must be present. Here, we report that O-GlcNAcase, which is responsible for the removal of O-GlcNAc additions on nuclear and cytosolic proteins, possesses intrinsic histone acetyltransferase (HAT) activity in vitro. Free as well as reconstituted nucleosomal histones are substrates of this bifunctional enzyme. This protein, now termed NCOAT (nuclear cytoplasmic O-GlcNAcase and acetyltransferase) has a typical HAT domain that has both active and inactive states. This finding demonstrates that NCOAT may be regulated to reduce the state of glycosylation of transcriptional activators while increasing the acetylation of histones to allow for the concerted activation of eukaryotic gene transcription.
Highlights
The genomes of eukaryotes are assembled into the highly condensed structure of chromatin
The histone acetyltransferase (HAT) activity, as measured by scintillation counting, of the O-GlcNAcase expressed in mammalian cells, but not that expressed in E. coli, was comparable with that obtained when using CBP
HAT activity is required to open the chromatin structure as part of the process of gene activation
Summary
We report that O-GlcNAcase does possess acetyltransferase activity in vitro for a synthetic histone substrate tail as well as for free core histones and reconstituted oligonucleosome substrates. The HAT activity is regulated and can only be observed when the enzyme is expressed in mammalian cells. The active site for this domain lies in the C terminus of the protein, where it resembles other acetyltransferases both structurally and in catalytic mechanism and has complete functional distinction from the N-terminal O-GlcNAcase domain. Because the enzyme is bifunctional with two important enzymatic domains, we have renamed it nuclear cytoplasmic O-GlcNAcase and acetyl transferase (NCOAT)
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