J. Biol. Chem., Vol. 265, Issue 36, 22300-22305, Dec, 1990
Interaction of the Mnt repressor with 37-base pair synthetic operator DNA fragments. Importance of symmetric GC pairs
GV Rajendrakumar, KN Ganesh and D Chatterji
Centre for Cellular and Molecular Biology, Hyderabad, India.
Mnt repressor is indirectly responsible for the maintenance of lysogeny of
the phage P22. This repressor interacts with a 21-base pair operator DNA
constituting within it a 17-base pair perfect 2-fold symmetric sequence
whose bases make a direct contact with the protein. We have synthesized six
37-base pair DNAs consisting of 21 base pair natural operator and its
modifications in which certain symmetrically situated GC base pairs were
replaced systematically with ATs to understand their importance. The
binding interaction studies of Mnt repressor to such natural and modified
operator DNAs reported here indicate that the GCs close to the center of
symmetry make major contacts with the protein whereas, GCs nearer to the
periphery form weak contacts. Methylation protection experiments indicated
that when the GCs near the center of symmetry were replaced with AT, the
central GC became more accessible for dimethyl sulfate methylation with
possible conformational change in DNA. The circular dichroism studies
indicated that upon repressor binding conformational changes in DNA takes
place with a possible increase in helicity of the repressor protein.
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