The DNA is bent and unwound, and the center Y₃R₄ step shows an unusual conformation. Below is a morph between B form DNA and the DNA bound to HincII (GTCGAC). The DNA is bend and unwound.

The distortion involves unstacking of the C₃ from the G₄ in the same strand, and the increase in stacking of the two G₄'s from each strand. This increased stacking is often seen in A form DNA and is known as a cross-strand purine stack (CSPS):

The DNA distortion was found to be important for sequence discrimination by HincII using two sets of experiments:
1. By removing the only direct contact or 'readout' of the center Y₃R₄ step using a mutant version of the enzyme: N141A HincII
2. By altering the way in which HincII distorts DNA with the Q138F mutant version of HincII

Horton Lab Homepage
Department of Biochemistry and Molecular Biophysics
University of Arizona
nhorton@u.arizona.edu
http://www.biochem.arizona.edu/horton/index.html

January 11, 2008

All contents copyright ©2008
All rights reserved.