High Quality Content by WIKIPEDIA articles! Sp1, also known as Specificity Protein 1, is a human transcription factor involved in gene expression in the early development of an organism. It belongs to the Sp/KLF family of transcription factors. The protein is 785 amino acids long, with a molecular weight of 81 kDA. 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 bind 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.