Nucleosomes are important for gene regulation, but comprehensive studies of nucleosome positioning, remodeling, and transcription factor binding at inducible mammalian promoters have not been reported. We have analyzed the IL-12 p40 promoter, which is induced in macrophages by bacterial products. High-resolution micrococcal nuclease analyses revealed that a positioned nucleosome, nucleosome 1, spans the promoter, with three positioned nucleosomes further upstream. Upon activation, nucleosome 1 was rapidly and selectively remodeled in a protein synthesis-dependent manner. In primary macrophages, IFNγ synergistically enhanced p40 expression, but little effect on remodeling or promoter occupancy was observed. These results suggest that remodeling complexes are selectively targeted to a single, promoter- encompassing nucleosome and that IFNγ influences an event that is independent or downstream of remodeling.