Stabilization of tetrahelical DNA by the quadruplex DNA binding protein QUAD.
The 57-kDa hepatic nuclear protein QUAD binds tightly and specifically a parallel tetrahelical form of the IgG switch region DNA (Weisman-Shomer, P. and Fry, M. (1993) J. Biol Chem. 268, 3306-3312). Here we show that QUAD is a heat-stable protein, maintaining approximately 90% of its tetrahelix binding activity after 10 min at 100 degrees C and becoming fully inactivated only after 30 min at 100 degrees C. To demonstrate that QUAD protects bound quadruplex DNA, naked and QUAD-bound tetrahelices were boiled, the protein residue in the complex was digested with trypsin and quadruplex and single-strand forms of the DNA component were resolved by electrophoresis. Whereas naked quadruplex DNA became fully denatured after 2 min at 100 degrees C, 55% of the QUAD-bound DNA was conserved as a tetrahelix after 6 min at 100 degrees C. These findings support the proposal that QUAD may act in vivo to stabilize tetrahelical DNA.
Weisman-Shomer
P
P
Unit of Biochemistry, Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
Fry
M
M
D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D006358:Hot Temperature; D008969:Molecular Sequence Data; D009691:Nucleic Acid Denaturation
D004268:DNA-Binding Proteins; C079561:QUAD protein, Oryctolagus cuniculus; D004247:DNA