Molecular Basis of the Selective Assembly of Functionally Distinct PRC1s - PROJECT SUMMARY/ABSTRACT
PROBLEM: Polycomb repressive complex 1 (PRC1) is a multi-protein assembly that epigenetically regulates
chromatin, which when misregulated, results in cancer. Originally identified in Drosophila as a four-component
complex, PRC1 has expanded its membership and functional repertoire over evolution. An important
unanswered question concerning human PRC1 is how certain combinations of PRC1 proteins assemble while
others do not, and how the types of PRC1s formed change during cellular differentiation. PRC1 assembly is
currently understood to occur through a series of 1:1 protein-protein interactions. This view, unfortunately,
does not explain how the protein-protein interaction of one PRC1 domain can somehow influence the binding
selectivity of another, seemingly unrelated protein-protein interaction. We have identified novel interactions
secondary to the known 1:1 direct interactions that provide selective checkpoints for including specific protein
combinations thereby allowing selective PRC1 assemblies. OBJECTIVE: We will systematically characterize
these secondary protein-protein interactions then investigate its role in the assembly and function of the distinct
PRC1s. METHODS: We will use biophysical methods (X-ray crystallography, analytical ultracentrifugation,
biolayer interferometry) to dissect the molecular basis of these selective assemblies. The functional
consequences of the secondary interactions that form these assemblies will be assessed using a novel FRET-
based histone modification assay. SIGNIFICANCE: Gene regulation is performed by many different proteins,
all of which work within multi-component systems. Current genomic approaches to investigating gene
regulation, while informative, lack a molecular perspective of protein-protein interactions necessary for a
complete understanding of these systems. We propose to fill this gap by determining how specific PRC1s
assemble and function. By defining the molecular choreography underlying PRC1 assembly, we will provide a
new perspective on the regulation and function of these complexes in genome regulation. Our results may
also be broadly applicable for understanding other gene regulatory systems, many of which utilize multi-
component systems with different homolog combinations.
