Virulence of the opportunistic pathogen Candida albicans correlates with the transition from a single-cell form to a filamentous form. As some of the pathways regulating this dimorphic switch are conserved in the model organism Saccharomyces cerevisiae, the authors of this study introduced genome-wide deletion alleles into a filamentous strain of S. cerevisiae to identify the genes controlling this phenotype. They identified a set of core genes, many of which encode proteins that regulate the expression of Flo11, one of the key proteins for filamentous growth. Included in this set was the previously uncharacterized gene MFG1, which encodes a protein that was shown to physically interact with two FLO11 transcriptional regulators, Flo8 and Mss11. Deletion of the MFG1 orthologue in C. albicans inhibited filamentation, biofilm formation and invasive growth, and the mutant was less virulent in an in vivo infection model. These data suggest that Mfg1 forms part of the conserved circuitry regulating fungal filamentation and pathogenesis.