SNAPc SNAPc:Oct-1:Staf:Type 3 Promoter Complex DNA with RNA Polymerase III Type 3 Closed Promoter Binding of SNAPc, Oct-1, and Staf to Type 3 Promoter Authored: Hernandez, N, 2003-09-11 07:42:29 Edited: Gillespie, ME, 0000-00-00 00:00:00 Reactome Database ID Release 4383791 Reactome, http://www.reactome.org ReactomeREACT_1607 SNAPc binds specifically to the PSE. This binding is mediated in part by an unusual Myb domain within SNAP190 (Mittal et al., 1999; Wong et al., 1998). However, even though a SNAP190 segment consisting of just the Myb domain binds DNA, within the complex the Myb domain is not sufficient for binding. The smallest characterized subassembly of SNAPc subunits that binds specifically to DNA consists of SNAP190 aa 84-505, SNAP43 aa 1-268, and SNAP50 (Ma and Hernandez, 2000). Consistent with the requirement for parts of SNAP190 and SNAP50 for DNA binding, UV cross-linking experiments suggest that both SNAP190 (Yoon et al., 1995) and SNAP50 (Henry et al., 1996) are in close contact with DNA.<p>The binding of SNAPc to the PSE is stabilized by a number of cooperative interactions with other members of the transcription initiation complex including Oct-1, TBP, and Brf2.<p>The binding of SNAPc to the core promoter is stabilized by a direct protein-protein contact with the Oct-1 POU domain.<p>SNAPc does not bind very efficiently to the PSE on its own. It contains a damper of DNA binding that resides within the C-terminal two thirds of SNAP190 and/or SNAP45, because a subcomplex of SNAPc (mini-SNAPc) lacking these sequences binds much more efficiently to DNA than complete SNAPc (Mittal et al., 1999). The damper within SNAPc is deactivated, probably through a conformational change, by a direct protein-protein contact with the Oct-1 POU domain. The transcription initiation complex is illustrated in Figure 6. The protein-protein contact between the Oct-1 POU domain and SNAPc involves a glutamic acid at position 7 within the Oct-1 POUS domain and a lysine at position 900 within SNAP190, which are symbolized in Figure 6 by small triangles (Ford et al., 1998; Hovde et al., 2002; Mittal et al., 1999). The octamer sequence within the DSE and the PSE are separated by more than 150 base pairs, but the direct protein-protein contact is rendered possible by the presence of a positioned nucleosome between the DSE and the PSE, which, as shown in the figure, probably brings into close proximity the Oct-1 POU domain and SNAPc (Stunkel et al., 1997; Zhao et al., 2001).