Mrf-2 is a member of a new class of DNA-binding proteins known as the AT-ri
ch interaction domain family or ARID. Chemical shift indices and characteri
stic NOE values indicate that the three-dimensional structure of the Mrf-2
ARID in complex with DNA is nearly identical to that of the free protein. T
he backbone dynamics of the Mrf-2 domain free and in complex with DNA have
been characterized by N-15 NMR relaxation measurements and model-free analy
sis. Chemical shift perturbations and dynamic studies suggest that two flex
ible interhelical loops, the flexible C-terminal tail, and one alpha -helix
are involved in DNA recognition, indicating the importance of protein dyna
mics in DNA binding. Some well-structured regions, in particular the putati
ve DNA-contacting helix, in Mrf-2 show a decrease in the order parameters (
S-2) upon complex formation. The less well-structured loops and the unstruc
tured C-terminus show reduced flexibility upon DNA binding. In addition, th
e model-free analysis indicates motions on the picosecond to nanosecond and
micro- to millisecond time scales at the DNA-binding surface of the bound
Mrf-2 ARID, suggesting a model where interactions between the protein and D
NA are highly dynamic.