DNA minor groove sensing and widening by the CCAAT-binding complex

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• The CCAAT box is a crucial eukaryotic promoter element involved in gene transcription regulation.
• The heterotrimeric CCAAT-binding complex (CBC) recognizes the CCAAT box, playing a key role in promoter organization.

Purpose of the Study:

• To elucidate the structural basis of CCAAT-binding complex (CBC) interaction with DNA.
• To understand the mechanism of sequence-specific DNA recognition by the CBC.

Main Methods:

• X-ray crystallography was used to determine the structures of the CBC from Aspergillus nidulans.
• Structures were solved in both the absence and presence of double-stranded DNA at 1.8 Å resolution.
• Biochemical data were utilized to support structural findings.

Main Results:

• Histone-like subunits HapC and HapE induce nucleosome-like DNA bending through interactions with the sugar-phosphate backbone.
• Subunit HapB tightly anchors the CBC to the CCAAT box via minor groove sensing and widening.
• Specific DNA duplex interactions with HapB explain the sequence specificity of the CBC.

Conclusions:

• The study reveals the detailed molecular mechanism of transcription factor binding to the CCAAT box.
• The findings explain how histone-like proteins achieve sequence specificity for promoter elements.
• This work provides insights into the fundamental processes of eukaryotic transcription regulation.