Transcriptional factor that can act as an activator or repressor depending on post-translational modifications. Binds to GT and GC boxes promoter elements. Competes with SP1 for the GC-box promoters. Weak activator of transcription (By similarity). Required for activation of SPARC transcription. Interacts with HDAC1 and HDAC2; the interaction deacetylates SP3 and regulates its transcriptional activity (By similarity). Interacts with v-Jun. Localizes to the nuclear periphery and in nuclear dots when sumoylated. Some localization in PML nuclear bodies (By similarity). The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors. Acetylated by histone acetyltransferase p300, deacetylated by HDACs. Acetylation/deacetylation states regulate transcriptional activity. Acetylation appears to activate transcription. Alternate sumoylation and acetylation at Lys-541 also control transcriptional activity. Sumoylation represses transcriptional activity. Lys-541 is the major site. Sumoylation at this site promotes nuclear localization to the nuclear periphery, nuclear dots and PML nuclear bodies. Alternate sumoylation and acetylation at Lys-541 also control transcriptional activity (By similarity). Belongs to the Sp1 C2H2-type zinc-finger protein family.