Nucleic Acids Research, Vol 26, Issue 6 1408-1413, Copyright © 1998 by Oxford University Press
M Sieber and RK Allemann
By designing recombinant genes containing tandem copies of the coding
region of the BHLH domain of MASH-1 (MASH-BHLH) with intervening DNA
sequences encoding linker sequences of 8 or 17 amino acids, the two
subunits of the MASH dimer have been connected to form the single chain
dimers MM8 and MM17. Despite the long and flexible linkers which connect
the C-terminus of the first BHLH subunit to the N-terminus of the second, a
distance of approximately 55 A, the single chain dimers could be produced
in Escherichia coli at high levels. MM8 and MM17 were monomeric and no
'cross-folding' of the subunits was observed. CD spectroscopy revealed
that, like wild-type MASH-BHLH, MM8 and MM17 adopt only partly folded
structures in the absence of DNA, but undergo a folding transition to a
mainly alpha-helical conformation on DNA binding. Titrations by
electrophoretic mobility shift assays revealed that the affinity of the
single chain dimers for E box-containing DNA sequences was increased
approximately 10-fold when compared with wild- type MASH-BHLH. On the other
hand, the affinity for heterologous DNA sequences was increased only
5-fold. Therefore, the introduction of the peptide linker led to a 4-fold
increase in DNA binding specificity from -0.14 to -0.57 kcal/mol.
ARTICLES
Single chain dimers of MASH-1 bind DNA with enhanced affinity
Laboratory for Organic Chemistry, Department of Chemistry, ETH-Zurich, Universitatstrasse 16, CH-8092 Zurich, Switzerland.
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