BACKGROUND: Canonical Notch signaling is initiated when ligand binding induces 
proteolytic release of the intracellular part of Notch (ICN) from the cell 
membrane. ICN then travels into the nucleus where it drives the assembly of a 
transcriptional activation complex containing the DNA-binding transcription 
factor CSL, ICN, and a specialized co-activator of the Mastermind family. A 
consensus DNA binding site motif for the CSL protein was previously defined 
using selection-based methods, but whether subsequent association of Notch and 
Mastermind-like proteins affects the DNA binding preferences of CSL has not 
previously been examined.
PRINCIPAL FINDINGS: Here, we utilized protein-binding microarrays (PBMs) to 
compare the binding site preferences of isolated CSL with the preferred binding 
sites of CSL when bound to the CSL-binding domains of all four different human 
Notch receptors. Measurements were taken both in the absence and in the presence 
of Mastermind-like-1 (MAML1). Our data show no detectable difference in the DNA 
binding site preferences of CSL before and after loading of Notch and MAML1 
proteins.
CONCLUSIONS/SIGNIFICANCE: These findings support the conclusion that accrual of 
Notch and MAML1 promote transcriptional activation without dramatically altering 
the preferred sites of DNA binding, and illustrate the potential of PBMs to 
analyze the binding site preferences of multiprotein-DNA complexes.