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The Transcriptional Coactivator SAYP Is a Trithorax Group Signature Subunit of the PBAP Chromatin Remodeling Complex

Gillian E. Chalkley,^1, Yuri M. Moshkin,^1, Karin Langenberg,¹ Karel Bezstarosti,² Andras Blastyak,³ Henrik Gyurkovics,³ Jeroen A. A. Demmers,² and C. Peter Verrijzer^1*

Department of Biochemistry, Center for Biomedical Genetics,¹ Proteomics Center, Erasmus University Medical Center, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands,² Hungarian Academy of Sciences, Biological Research Center, Institute of Genetics, H-6701 Szeged, Hungary³

Received 14 December 2007/ Returned for modification 7 February 2008/ Accepted 19 February 2008

SWI/SNF ATP-dependent chromatin remodeling complexes (remodelers) perform critical functions in eukaryotic gene expression control. BAP and PBAP are the fly representatives of the two evolutionarily conserved major subclasses of SWI/SNF remodelers. Both complexes share seven core subunits, including the Brahma ATPase, but differ in a few signature subunits; POLYBROMO and BAP170 specify PBAP, whereas OSA defines BAP. Here, we show that the transcriptional coactivator and PHD finger protein SAYP is a novel PBAP subunit. Biochemical analysis established that SAYP is tightly associated with PBAP but absent from BAP. SAYP, POLYBROMO, and BAP170 display an intimately overlapping distribution on larval salivary gland polytene chromosomes. Genome-wide expression analysis revealed that SAYP is critical for PBAP-dependent transcription. SAYP is required for normal development and interacts genetically with core- and PBAP-selective subunits. Genetic analysis suggested that, like BAP, PBAP also counteracts Polycomb silencing. SAYP appears to be a key architectural component required for the integrity and association of the PBAP-specific module. We conclude that SAYP is a signature subunit that plays a major role in the functional specificity of the PBAP holoenzyme.

Published ahead of print on 25 February 2008.

These authors contributed equally to this work and should both be considered first authors.