Phosphorylation of Heterochromatin Protein 1 by Casein Kinase II Is Required for Efficient Heterochromatin Binding inDrosophila

doi:10.1074/jbc.274.21.15095

Phosphorylation of Heterochromatin Protein 1 by Casein Kinase II Is Required for Efficient Heterochromatin Binding inDrosophila*

Tao Zhao and
Joel C. Eissenberg‡

From the Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University Health Sciences Center, St. Louis, Missouri 63104-1079

Abstract

Heterochromatin-associated protein 1 (HP1) is a nonhistone chromosomal protein with a dose-dependent effect on heterochromatin mediated position-effect silencing. It is multiply phosphorylated in vivo. Hyperphosphorylation of HP1 is correlated with heterochromatin assembly. We report here that HP1 is phosphorylated by casein kinase II in vivo at three serine residues located at the N and C termini of the protein. Alanine substitution mutations in the casein kinase II target phosphorylation sites dramatically reduce the heterochromatin binding activity of HP1, whereas glutamate substitution mutations, which mimic the charge contributions of phosphorylated serine, have apparently wild-type binding activity. We propose that phosphorylation of HP1 promotes protein-protein interaction between HP1 and target binding proteins in heterochromatin.

Footnotes

↵* This project was supported by National Science Foundation Grant IBN 9506103.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ To whom correspondence should be addressed: Edward A. Doisy Dept. of Biochemistry and Molecular Biology, St. Louis University Health Sciences Center, 1402 South Grand Blvd., St. Louis, MO 63104-1079. Tel.: 314-577-8154; Fax: 314-577-8156; E-mail:eissenjc{at}wpogate.slu.edu.
↵2 C. V. C. Glover, personal communication.
↵3 T. Zhao and J. C. Eissenberg, unpublished observations.
Abbreviations:

HP1

heterochromatin-associated protein 1

dHP1

HP1 fromDrosophila

rHP1

recombinant HP1

CKII

casein kinase II

FPLC

fast protein liquid chromatography

PAGE

polyacrylamide gel electrophoresis

X-gal

5-bromo-4-chloro-3-indolyl β-d-galactopyranoside

HPLC

high pressure liquid chromatography
- Received December 28, 1998.
- Revision received March 1, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.