Specificity protein 1 (Sp1) was first identified by cell fractionation procedures
and shown to interact with GC and GT oligonucleotide sequences that
are typically found in diverse viral and cellular gene promoters (1–6). The Sp1
gene was first cloned by Kadonaga and coworkers, and the various functional
domains of Sp1 were determined in a series of in vitro and whole cell assays. A
schematic representation of the functional domains of Sp1 is given in Fig. 1.
These domains include an N-terminal A- and a central B-domain which contain
S/T- and Q-rich regions that are important for transactivation (7–10). Within the
C- and D-domains near the C-terminal region of Sp1, there are three highly
characteristic zinc fingers required for sequence-specific DNA binding.