A manifestation of Alzheimer's disease is the presence of amyloid depositions in brains of afflicted individuals. A major component of these depositions is the amyloid beta-protein, which is a truncated form of the larger amyloid beta-protein precursor (APP). To investigate the regulation of APP gene expression, the APP promoter and selected deletions were placed 5' to the reporter gene chloramphenicol acetyltransferase. The promoter deletions were transfected into different cell lines that showed variant levels of endogenous APP transcripts. Transient transfection assays showed that 96 base pairs 5' to the transcriptional start site are sufficient for cell type-specific promoter activity. A nuclear factor that binds to this region in a sequence-specific manner was identified by mobility shift electrophoresis, DNase footprinting, and methylation interference. The DNase-protected region covers about 25 base pairs on both strands (position -31 to -55). Mutations within this domain revealed a sequence of 12 base pairs that is crucial for factor binding. This sequence overlaps with the consensus sequences for transcription factors AP-1 and AP-4. However, competition experiments suggest that the nuclear factor that binds to the APP promoter is distinct from both AP-1 and AP-4. Factor binding to the characterized recognition sequence is observed in nuclear extracts originating from human, mouse, and rat cells, suggesting a high degree of conservation.