Transcription factor TFIID is a multiprotein complex composed of the TATA box-binding protein (TBP) and multiple TBP-associated factors (TAFs). TFIID plays an essential role in mediating transcriptional activation by gene-specific activators. Numerous transcriptional activators have been characterized from mammalian cells; however, molecular analysis of the components of mammalian TFIID has been incomplete. Here we describe isolation of cDNAs encoding two TAF subunits of the human transcription factor TFIID. The first cDNA is predicted to encode the C-terminal 947 residues of the 130-kDa human TAF subunit, hTAFII130. The second cDNA encodes the C-terminal 801 residues of the 100-kDa subunit, hTAFII100. Recombinant TAFs expressed in human cells by transient transfections are capable of associating with the endogenous TAFs and TBP to form a TFIID complex in vivo. Protein binding experiments demonstrate that hTAFII130, like its Drosophila homolog dTAFII110, interacts with the glutamine-rich activation domains of the human transcription factor Sp1. Furthermore, hTAFII130 shows reduced binding to the Sp1 mutants with impaired ability to activate transcription, suggesting a role for hTAFII130 as a direct coactivator target for Sp1.