Nucleosome binding by the constitutive transcription factor Sp1.

The constitutive transcription factor Sp1 plays a role in the transcription of numerous viral and cellular genes including constitutive "housekeeping" genes and inducible genes. Sp1 has also been implicated in the formation of a nucleosome-free region in Simian virus 40 (SV40) minichromosomes. To investigate the potential functions of Sp1 in remodeling chromatin structures, Sp1 was analyzed for the ability to bind its recognition sites (GC boxes) in DNA fragments reconstituted into nucleosome cores. Sp1 was found to bind to the GC boxes of the SV40 early promoter when this element was reconstituted into nucleosome cores. The affinity of Sp1 for the nucleosomal SV40 early promoter DNA was reduced approximately 10-20-fold relative to naked DNA. A peptide containing only the zinc fingers of Sp1 was also capable of binding nucleosomal DNA, indicating that the glutamine-rich and serine/threonine-rich domains of Sp1 are not required for nucleosome binding. The binding of Sp1 to nucleosome cores resulted in the formation of a ternary Sp1-nucleosome complex.