Fos-Jun heterodimers and Jun homodimers bend DNA in opposite orientations: implications for transcription factor...

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The AP-1 transcription factor binding site is crucial for regulating gene expression.
• Fos and Jun proteins form heterodimers and homodimers that bind to the AP-1 site.
• Understanding the structural consequences of these interactions is key to deciphering gene regulation.

Purpose of the Study:

• To investigate the conformational changes induced in the DNA helix by Fos-Jun heterodimers and Jun homodimers.
• To determine the orientation and magnitude of DNA bending mediated by these protein complexes.
• To elucidate how different domains of Fos and Jun proteins contribute to DNA bending.

Main Methods:

• Circular permutation analysis to assess DNA flexure induced by protein binding.
• Phasing analysis to determine the orientation of DNA bending (major or minor groove).
• Use of full-length proteins and truncated peptides (dimerization and DNA-binding domains) to map functional regions.

Main Results:

• Both Fos-Jun heterodimers and Jun homodimers induce significant flexure at the AP-1 site.
• Fos-Jun heterodimers bend DNA towards the major groove.
• Jun homodimers bend DNA towards the minor groove, indicating opposite orientations.
• Specific protein domains influence the magnitude of the DNA bend angle.

Conclusions:

• Fos-Jun heterodimers and Jun homodimers form topologically distinct DNA-protein complexes despite sequence similarities.
• The orientation of DNA bending is a critical determinant of complex formation and function.
• Differential DNA bending by Fos-Jun and Jun homodimers contributes to the specificity of gene regulation.