Mastermind (Mam) is a component of Notch pathway signaling. In combination with 
the intracellular domain of Notch and Suppressor of Hairless, Mam forms a 
transcriptional activation complex. We have initiated a genetic approach to 
identify other loci involved in Mam function. The screen utilizes engineered 
mutations in Mam that derive from GAL4-UAS-directed expression of dominant 
negative constructs. When driven at the wing margin, truncated versions of Mam 
phenocopy Notch pathway mutations. Correlated with these phenotypes is 
depression of Notch pathway target expression. Strains expressing truncated 
versions of Mam were tested for genetic interactions with a large collection of 
chromosomal deficiencies. Genomic segments that enhanced and suppressed the 
dominant wing phenotype were identified. These regions may contain 
uncharacterized loci involved in Notch pathway function.