The gene pannier acts as a repressor of achaete and scute, two transcription factors expressed in discrete subsets of cells at the sites where neural precursors develop. Molecular analysis of mutant alleles revealed the presence of two functional domains within the pannier protein: a zinc finger domain showing homology to the GATA-1 family of vertebrate transcription factors and a domain comprising two putative amphipathic helices. Mutants associated with lesions in the zinc finger domain display an overexpression of achaete and scute and the development of extra neural precursors. Mutant proteins in which the domain including the putative helices is deleted act as hyperactive repressor molecules causing a loss of achaete/scute expression and a loss of neural precursors. Other results suggest that the activity of pannier may be modulated by association with position-specific factors.