Site-specific transcription factors of the nuclear factor 1 (NF1) family are ubiquitous, are encoded by four genes in mammals, and play a role in regulating transcription of approximately 100 cell and viral genes. The NF1 proteins are characterized by the ability to act as both transcription factors and viral replication factors and by a low affinity for nucleosomal DNA. The review considers the dual role of the NF1 family factors in hormone-mediated transactivation of the mouse mammary tumor virus (MMTV) promoter: the factors are essential for both transcription activation and nucleosome remodeling. Emphasis is placed on the role of the NF1 family factors in the formation and maintenance of a present chromatin structure in the MMTV promoter region and the regulatory elements of the lysozyme gene during macrophage differentiation. Since disruption of individual NF1 family genes causes pathological changes in human and animal tissues, the NF1 family proteins are subjects of basic and applied research.