NRG1, a repressor of filamentous growth in C.albicans, is down-regulated during filament induction

In response to a variety of external signals, the fungal pathogen Candida a lbicans undergoes a transition between ellipsoidal single cells (blastospor es) and filaments composed of elongated cells attached end-to-end. Here we identify a DNA-binding protein, Nrg1, that represses filamentous growth in Candida probably by acting through the co-repressor Tup1. nrg1 mutant cells are predominantly filamentous under non-filament-inducing conditions and t heir colony morphology resembles that of tup1 mutants. We also identify two filament-specific genes, ECE1 and HWP1, whose transcription is repressed b y Nrg1 under noninducing conditions. These genes constitute a subset of tho se under Tup1 control, providing further evidence that Nrg1 acts by recruit ing Tup1 to target genes. We show that growth in serum at 37 degreesC, a po tent inducer of filamentous growth, causes a reduction of NRG1 mRNA, sugges ting that filamentous growth is induced by the down-regulation of NRG1. Con sistent with this idea, expression of NRG1 from a non-regulated promoter pa rtially blocks the induction of filamentous growth.