5J8Y: Crystal Structure Of The Scm-sam And Sfmbt-sam Heterodimer

Polycomb group (PcG) protein complexes repress transcription by modifying target gene chromatin. In Drosophila, this repression requires association of PcG protein complexes with cis-regulatory Polycomb response elements (PREs), but the interactions permitting formation of these assemblies are poorly understood. We show that the Sfmbt subunit of the DNA-binding Pho-repressive complex (PhoRC) and the Scm subunit of the canonical Polycomb-repressive complex 1 (PRC1) directly bind each other through their SAM domains. The 1.9 A crystal structure of the Scm-SAM:Sfmbt-SAM complex reveals the recognition mechanism and shows that Sfmbt-SAM lacks the polymerization capacity of the SAM domains of Scm and its PRC1 partner subunit, Ph. Functional analyses in Drosophila demonstrate that Sfmbt-SAM and Scm-SAM are essential for repression and that PhoRC DNA binding is critical to initiate PRC1 association with PREs. Together, this suggests that PRE-tethered Sfmbt-SAM nucleates PRC1 recruitment and that Scm-SAM/Ph-SAM-mediated polymerization then results in the formation of PRC1-compacted chromatin.
PDB ID: 5J8YDownload
MMDB ID: 139407
PDB Deposition Date: 2016/4/8
Updated in MMDB: 2016/05
Experimental Method:
x-ray diffraction
Resolution: 1.98  Å
Source Organism:
Similar Structures:
Biological Unit for 5J8Y: dimeric; determined by author and by software (PISA)
Molecular Components in 5J8Y
Label Count Molecule
Proteins (2 molecules)
Polycomb Protein SCM(Gene symbol: Scm)
Molecule annotation
Polycomb Protein Sfmbt(Gene symbol: Sfmbt)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB