Interaction between isolated transcriptional activation domains of Sp1 revealed by heteronuclear magnetic resonance

<jats:title>Abstract</jats:title><jats:p>The promoter‐specific transcription factor Sp1 is expressed ubiquitously, and plays a primary role in the regulation of the expression of many genes. Domains A and B located in the N‐terminal half of the protein are characterized by glutamine‐rich (Q‐rich) sequences. These Q‐rich domains have been shown to be involved in the interaction between Sp1 and different classes of nuclear proteins, such as TATA‐binding protein associated factors. Furthermore, the self‐association of Sp1 via Q‐rich domains is also important for the regulation of transcriptional activity. It has been considered that an Sp1 molecule bound to a “distal” GC‐box synergistically interacts with another Sp1 molecule at a “proximal” binding site. Although the formation of multimers via Q‐rich domains seems functionally important for Sp1, little is known about the structural and physicochemical nature of the interaction between Q‐rich domains. We analyzed the structural details of isolated glutamine‐rich B (QB) domains of Sp1 by circular dichroism (CD), analytical ultracentrifugation, and heteronuclear magnetic resonance spectroscopy (NMR). We found the isolated QB domains to be disordered under all conditions examined. Nevertheless, a detailed analysis of NMR spectra clearly indicated interaction between the domains. In particular, the C‐terminal half was responsible for the self‐association. Furthermore, analytical ultracentrifugation demonstrated weak but significant interaction between isolated QB domains. The self‐association between QB domains would be responsible, at least in part, for the formation of multimers by full‐length Sp1 molecules that has been proposed to occur during transcriptional activation.</jats:p>