C-13-NMR RELAXATION STUDY ON MOBILITY OF THE DNA-BINDING ARM OF HU

The mobility of the DNA-binding arm of HU protein was studied by C-13-NMR spectroscopy. The correlation times tau(c) Of Phe47C alpha in the body and Gly60C alpha in the arm of HU were determined for HU and HU-DNA complex. The value of tau(c) of Phe47C alpha is 2-4 times larger than that of Gly60C alpha irrespective of the presence or absence of DNA. These results show that Gly60C alpha undergoes more rapid motion than Phe47C alpha. The increase in correlation time on addition of DNA is greater for Gly60C alpha than for Phe47C alpha. This suggests that the addition of DNA influences more significantly the motion of Gly60C alpha than that of Phe47C alpha. These results are in accord with the X-ray result, in which the top part of the arm is not visible. Gly60C alpha in the arm is thus more mobile than Phe47C alpha in the body, and the mobility of Gly60C alpha is reduced by the DNA binding.