The eukaryotic transcription factor Sp1 is a sequence-specific DNA-binding
protein that binds to GC-rich sequences in a large number of promoters. Des
pite its ubiquitous nature, Sp1 (and related factors) can modulate transcri
ption of specific genes through interactions with cell type or stage-specif
ic transcription factors. Sp1 can also directly influence formation of the
transcription initiation complex. Furthermore, binding of Sp1 at distal pro
moter elements can affect formation of active chromatin structures. Thus th
e Sp1 family of proteins plays a crucial role in gene regulation in higher
organisms.