Chromatin structure analysis of the human c-fos promoter reveals a centrally positioned nucleosome.

Chromatin architecture plays an important regulatory role in nuclear transcription in eukaryotes. In particular, a preset chromatin organization has been proposed to prime rapidly inducible genes for response to extracellular signals. We analyzed the chromatin architecture of the rapidly inducible human c-fos gene using a combination of nuclease digestion studies. Several regions of nuclease sensitivity in the c-fos gene are observed: (i) a hypersensitive site at position -1900; (ii) a region centered at -350 that corresponds to the locations of the serum response element (SRE) and the sis-inducible element (SIE); (iii) a region around the transcriptional start site that includes the TATA box, the cAMP-responsive element (CRE) and a directly repeated sequence (DRE); and (iv) two sites at positions +250 and +550 that appear to delineate the linker regions of two positioned nucleosomes. In contrast, the region from -280 to -90 is strongly resistant to nuclease digestion. We identify a highly positioned nucleosome in this region of the c-fos promoter that may contribute to a defined higher-order nucleoprotein structure containing the nucleosome and proteins bound to the SIE, SRE, DRE, and CRE elements and TATA box. This structure may lead to a functional juxtaposition of the regulatory elements of the c-fos promoter and suggests that such a chromatin architecture is particularly suited for presetting promoters for rapid responsiveness.