Dynamic exchange at regulatory elements during chromatin remodeling underlies assisted loading mechanism

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Eukaryotic transcription factors, including the glucocorticoid receptor (GR), regulate gene expression through interactions with DNA.
• Previous photobleaching experiments suggest transient DNA binding of GR on the scale of seconds, implying sparse occupancy of response elements.

Purpose of the Study:

• To investigate the binding dynamics of glucocorticoid receptors (GR) at DNA response elements.
• To determine if GR binding influences the steady-state binding of other receptor variants at the same site.

Main Methods:

• Experimental analysis of receptor binding in living cells.
• Mathematical simulations to model transcription factor-DNA interactions and residency times.

Main Results:

• The binding of one GR does not impede the steady-state binding of another GR variant to the same glucocorticoid response element (GRE).
• Mathematical models support noncompetitive binding, characterized by short GR/GRE residency times and infrequent DNA binding events.
• GR binding can increase chromatin accessibility, leading to enhanced binding of variant receptors, a phenomenon termed 'assisted loading'.

Conclusions:

• Sparse, transient transcription factor-DNA interactions can induce chromatin reorganization.
• This reorganization facilitates transient access for secondary regulatory factors, impacting gene expression regulation.