A tissue-specific MAR/SAR DNA-binding protein with unusual binding site recognition

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The nuclear matrix/scaffold-associating DNAs (MARs/SARs) play a role in genome organization.
• Understanding DNA-binding proteins is essential for deciphering gene regulation.

Purpose of the Study:

• To characterize the DNA-binding properties of the human DNA-binding protein SATB1.
• To elucidate the specific DNA sequence and structural features recognized by SATB1.

Main Methods:

• Cloning of human cDNA encoding SATB1.
• Missing nucleoside experiments to identify binding sequences.
• Mutation analysis to assess the importance of sequence features.
• Supercoiled DNA assays to evaluate unwinding potential.
• Chemical interference assays to determine binding location.

Main Results:

• SATB1 is predominantly expressed in the thymus and binds MARs/SARs.
• SATB1 selectively binds to AT-rich sequences with a specific strand composition (ATC sequences).
• Binding is dependent on the DNA's ability to form unpaired regions in supercoiled DNA.
• SATB1 interacts with the minor groove, suggesting indirect recognition of the DNA structure rather than direct base contact.

Conclusions:

• SATB1 recognizes specific DNA structural alterations within AT-rich sequences, not the bases directly.
• The binding mechanism involves the sugar-phosphate backbone and DNA unwinding potential.
• SATB1's unique binding properties are critical for its function, likely in thymus-specific gene regulation.