Sp1 (GC-box binding protein), GST tagged human

Sp1 is a sequence-specific DNA-binding protein and a eukaryotic transcription factor. It is a ubiquitously expressed nuclear protein. It is one of the first transcription factors to be identified, and the first whose gene was cloned. It was identified as a host factor in HeLa cells, which interacted with the GC-rich sites in SV40 (Simian virus 40) early promoter, and was crucial for in vitro transcription of this promoter. Sp1 is a single polypeptide chain composed of 778 amino acids, and has a molecular weight of 105kDa.

Sp1 was first detected in HeLa cells on the basis of its ability to activate the SV40 early promoter transcription. Subsequently it was shown to recognize and bind selectively to a GC-rich consensus sequence (GC-box: GGGCGG or CACCC) that presents in the promoter of several important cellular genes, including SV40 early, HIV-1, PDGF-B etc. Sp1 was the first transcription factor to be cloned and. Analysis of structure and function has revealed that Sp1 can be separated into discrete functional domains. The DNA-binding domain consists of three zinc fingers that specifically bind to the GC-box element. Sp1 contains at least four separate transcriptional activation domains. Two of these domains are glutamine-rich, a well-characterized motif found in several other transcription factors. In addition to transcription, Sp1 function has been linked to cell growth, cancer, Huntington disease and other disorders through transcriptional regulation or specific protein-protein interactions. The function of Sp1 can be regulated by phosphorylation and glycosylation.

Sp1 binds to GC-rich sequences in a wide variety of promoters. It interacts with cell type or stage-specific transcription factors, and thus, regulates transcription of specific genes. It also controls the formation of the transcription initiation complex. This protein plays a key role in controlling the basal levels of glutathione S-transferase (GSTP1) promoter and the expression of leukotriene C4 synthase gene in the THP-1, a monocyte-like cell line.

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