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Molecular and Cellular Biology, August 2005, p. 6578-6591, Vol. 25, No. 15
0270-7306/05/$08.00+0 doi:10.1128/MCB.25.15.6578-6591.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Richard B. Emmons,2,
Nicole J. Francis,1,2,
,
Brigitte Wild,3
Jürg Müller,3
Robert E. Kingston,1,2* and
Chao-ting Wu2*
Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114,1 Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115,2 EMBL, Gene Expression Programme, Meyerhofstrasse 1, 69120 Heidelberg, Germany3
Received 24 January 2005/ Returned for modification 8 March 2005/ Accepted 5 May 2005
Polycomb group (PcG) genes propagate patterns of transcriptional repression throughout development. The products of several such genes are part of Polycomb repressive complex 1 (PRC1), which inhibits chromatin remodeling and transcription in vitro. Genetic and biochemical studies suggest the product of the Posterior sex combs (Psc) gene plays a central role in both PcG-mediated gene repression in vivo and PRC1 activity in vitro. To dissect the relationship between the in vivo and in vitro activities of Psc, we identified the lesions associated with 11 genetically characterized Psc mutations and asked how the corresponding mutant proteins affect Psc activity on nucleosomal templates in vitro. Analysis of both single-mutant Psc proteins and recombinant complexes containing mutant protein revealed that Psc encodes at least two functions, complex formation and the inhibition of remodeling and transcription, which require different regions of the protein. There is an excellent correlation between the in vivo phenotypes of mutant Psc alleles and the structure and in vitro activities of the corresponding proteins, suggesting that the in vitro activities of PRC1 reflect essential functions of Psc in vivo.
These authors contributed equally to this work.
Present address: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138.
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