Structural homology between the Rap30 DNA-binding domain and linker histone H5: implications for preinitiation...

Area of Science:

• Structural Biology
• Molecular Biology
• Biochemistry

Background:

• The human Rap30 protein plays a role in the preinitiation complex assembly during transcription.
• Understanding the three-dimensional structure of Rap30's DNA-binding domain is crucial for elucidating its function.

Purpose of the Study:

• To determine the three-dimensional structure of the human Rap30 DNA-binding domain using NMR spectroscopy.
• To identify the DNA-binding surface and compare its structure to known DNA-binding proteins.
• To infer the functional role of Rap30 in transcription initiation based on its structural characteristics.

Main Methods:

• Multinuclear Nuclear Magnetic Resonance (NMR) spectroscopy was employed to solve the three-dimensional structure.
• Structural comparisons were made with existing databases and known protein structures, including linker histone H5 and HNF-3/fork head-DNA complexes.

Main Results:

• The globular domain of human Rap30 adopts a winged helix-turn-helix fold, classifying it among eukaryotic transcription factors.
• A DNA-binding surface was identified, showing consistency with the HNF-3/fork head-DNA complex structure, despite weak DNA interaction.
• Structural homology was noted between the Rap30 DNA-binding domain and region 4 of E. coli sigma70.

Conclusions:

• The Rap30 DNA-binding domain's structure suggests a role as a condensation factor in preinitiation complex assembly, analogous to linker histones in chromatin formation.
• Functional similarity to linker histones may explain Rap30's binding preference for bent DNA induced by the TATA box-binding protein.
• The observed homology indicates that prokaryotic sigma factors might also possess linker histone-like activity in forming transcription initiation complexes.