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Molecular and Cellular Biology, May 1999, p. 3624-3634, Vol. 19, No. 5
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Nonessential HP1-Like Protein Affects Starvation-Induced Assembly of Condensed Chromatin and Gene Expression in Macronuclei of Tetrahymena thermophila

Hui Huang,1 James F. Smothers,2,dagger Emily A. Wiley,2,dagger and C. David Allis2,*

Department of Biology, Syracuse University, Syracuse, New York 13244,1 and Department of Biology, University of Rochester, Rochester, New York 146272

Received 20 August 1998/Returned for modification 6 October 1998/Accepted 8 February 1999

Heterochromatin represents a specialized chromatin environment vital to both the repression and expression of certain eukaryotic genes. One of the best-studied heterochromatin-associated proteins is Drosophila HP1. In this report, we have disrupted all somatic copies of the Tetrahymena HHP1 gene, which encodes an HP1-like protein, Hhp1p, in macronuclei (H. Huang, E. A. Wiley, R. C. Lending, and C. D. Allis, Proc. Natl. Acad. Sci. USA 95:13624-13629, 1998). Unlike the Drosophila HP1 gene, HHP1 is not essential in Tetrahymena spp., and during vegetative growth no clear phenotype is observed in cells lacking Hhp1p (Delta HHP1). However, during a shift to nongrowth conditions, the survival rate of Delta HHP1 cells is reduced compared to that of wild-type cells. Upon starvation, Hhp1p becomes hyperphosphorylated concomitant with a reduction in macronuclear volume and an increase in the size of electron-dense chromatin bodies; neither of these morphological changes occurs in the absence of Hhp1p. Activation of two starvation-induced genes (ngoA and CyP) is significantly reduced in Delta HHP1 cells while, in contrast, the expression of several growth-related or constitutively expressed genes is comparable to that in wild-type cells. These results suggest that Hhp1p functions in the establishment and/or maintenance of a specialized condensed chromatin environment that facilitates the expression of certain genes linked to a starvation-induced response.

* Corresponding author. Present address: Department of Biochemistry and Molecular Genetics, 6222 Jordan Hall, University of Virginia H.S.C., 1300 Jefferson Park Ave., Charlottesville, VA 22908. Phone: (804) 243-6048. Fax: (804) 924-5069. E-mail: allis{at}virginia.edu.

dagger Present address: Fred Hutchinson Cancer Research Center, Seattle, WA 98109.

Molecular and Cellular Biology, May 1999, p. 3624-3634, Vol. 19, No. 5
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


This article has been cited by other articles:

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