Stabilization of tetrahelical DNA by the quadruplex DNA binding protein QUAD - PubMed (original) (raw)

. 1994 Nov 30;205(1):305-11.

doi: 10.1006/bbrc.1994.2665.

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Stabilization of tetrahelical DNA by the quadruplex DNA binding protein QUAD

P Weisman-Shomer et al. Biochem Biophys Res Commun. 1994.

Abstract

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.

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