Sp1

 Sp1 is a human transcription factor involved in gene expression in the early development of an organism. The protein is 785 amino acids long, with a molecular weight of 95 kDA. The full protein sequence can be found banked in the NCBI homepage, with the accession number NP_612482. The SP1 transcription factor contains a zinc finger protein motif, by which it binds directly to DNA and enhances gene transcription. Its zinc fingers are of the Cys2/His2 type and binds the consensus sequence 5'-(G/T)GGGCGG(G/A)(G/A)(C/T)-3' (GC box element). It was discovered in 1983 and has since been modified to form Sp1C, which has a zinc finger protein DNA binding domain.

In the SV40 virus, Sp1 binds to the GC boxes in the regulatory region(RR) of the genome.