Interactions between DNA, transcriptional regulator Dreb2a and the Med25 mediator subunit from Arabidopsis thaliana involve conformational changes

Abstract

Mediator is a multiprotein coregulatory complex that conveys signals from DNA-bound transcriptional regulators to the RNA polymerase II transcription machinery in eukaryotes. The molecular mechanisms for how these signals are transmitted are still elusive. By using purified transcription factor Dreb2a, mediator subunit Med25 from Arabidopsis thaliana, and a combination of biochemical and biophysical methods, we show that binding of Dreb2a to its canonical DNA sequence leads to an increase in secondary structure of the transcription factor. Similarly, interaction between the Dreb2a and Med25 in the absence of DNA results in conformational changes. However, the presence of the canonical Dreb2a DNA-binding site reduces the affinity between Dreb2a and Med25. We conclude that transcription regulation is facilitated by small but distinct changes in energetic and structural parameters of the involved proteins.

Arabidopsis GROWTH-REGULATING FACTOR7 Functions as a Transcriptional Repressor of Abscisic Acid– and Osmotic Stress–Responsive Genes, Including DREB2A

“…Subsequent research on DREB2A-INTERACTING PROTEIN1 and DRIP2 revealed their roles in the rapid degradation of DREB2A through 26S proteasome-dependent proteolysis under nonstress conditions (Qin et al, 2008). Recently, reports on Arabidopsis MEDIATOR25, a newly described DREB2A-interacting cofactor protein, suggested another method of regulation of DREB2A activation (Elfving et al, 2011;Blumberg et al, 2012).…”

Investigating the role of the Mediator complex in plant defence

“…These changes, combined with other signal pathways that cause posttranslational modifications of different transcription factors, might therefore determine the level of transcription from each gene (Blomberg et al, 2012). Consistent with this idea, Blomberg and colleagues have found that binding of DREB2A to its canonical DNA sequence leads to an increase in secondary structure of the transcription factor.…”

“…Surprisingly, Blomberg et al (2012) demonstrated that DREB2A from Arabidopsis can interact with the human MED25 ACID domain and displayed similar complex kinetics as the Arabidopsis MED25 ACID domain with DREB2A interaction. This result not only suggests that there is sequence similarity in the ACID domain between the two species, but also it proposes that whatever is discovered in plant gene regulation through the Mediators complex may be applied to the human Mediator complex.…”

“…Recently, an interaction between one of the Mediator complex subunits, MED25, and a number of TFs has been reported (Elfving et al, 2011;Blomberg et al, 2012;Chen et al, 2012;Cevik et al, 2012). Some of the TFs were known to play an important role in plant hormone signalling pathways during plant defence against pathogens (Chen et al, 2012;Cevik et al, 2012).…”

“…However, the presence of the canonical DREB2A DNAbinding site reduces the affinity between DREB2A and MED25. They stated that transcription regulation is facilitated by small but distinct changes in energetic and structural parameters of the involved proteins (Blomberg et al, 2012).…”