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Molecular and Cellular Biology, March 1999, p. 2061-2068, Vol. 19, No. 3
Department of Biochemistry and Molecular
Genetics, University of Virginia Health Sciences Center,
Charlottesville, Virginia 229081; Howard
Hughes Medical Institute, Department of Biochemistry and Molecular
Biology and The Center for Gene Regulation, The Pennsylvania State
University, University Park, Pennsylvania
16802-45002; Proscript Inc., Cambridge,
Massachusetts 018903; Department of
Microbiology and Immunology, Baylor College of Medicine, Houston,
Texas 770304; and Laval University
Cancer Research Center, Hôtel-Dies de Québec,
Québec QC G1R-2J6, Canada5
Received 4 August 1998/Returned for modification 1 October
1998/Accepted 1 December 1998
Recently, we reported the identification of a 55-kDa polypeptide
(p55) from Tetrahymena macronuclei as a catalytic subunit of a transcription-associated histone acetyltransferase (HAT A). Extensive homology between p55 and Gcn5p, a component of the SAGA and
ADA transcriptional coactivator complexes in budding yeast, suggests an
immediate link between the regulation of chromatin structure and
transcriptional output. Here we report the characterization of a second
transcription-associated HAT activity from Tetrahymena macronuclei. This novel activity is distinct from complexes containing p55 and putative ciliate SAGA and ADA components and shares several characteristics with NuA4 (for nucleosomal H2A/H4), a 1.8-MDa, Gcn5p-independent HAT complex recently described in yeast. A key feature of both the NuA4 and Tetrahymena activities is
their acetylation site specificity for lysines 5, 8, 12, and 16 of H4
and lysines 5 and 9 of H2A in nucleosomal substrates, patterns that are
distinct from those of known Gcn5p family members. Moreover, like NuA4, the Tetrahymena activity is capable of activating
transcription from nucleosomal templates in vitro in an acetyl coenzyme
A-dependent fashion. Unlike NuA4, however, sucrose gradient analyses of
the ciliate enzyme, following sequential denaturation and renaturation, estimate the molecular size of the catalytically active subunit to be
~80 kDa, consistent with the notion that a single polypeptide or a
stable subcomplex is sufficient for this H2A/H4 nucleosomal HAT
activity. Together, these data document the importance of this novel
HAT activity for transcriptional activation from chromatin templates
and suggest that a second catalytic HAT subunit, in addition to
p55/Gcn5p, is conserved between yeast and Tetrahymena.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
A Novel H2A/H4 Nucleosomal Histone
Acetyltransferase in Tetrahymena thermophila
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Genetics, University of Virginia Health
Sciences Center, Box 440, Charlottesville, VA 22908. Phone: (804)
243-6048. Fax: (804) 924-5069. E-mail: allis{at}virginia.edu.
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