SOLUTION STRUCTURE OF THE I-GAMMA SUBDOMAIN OF THE MU-END DNA-BINDINGDOMAIN OF PHAGE MU-TRANSPOSASE

The MuA transposase of phase Mu is a large modular protein that plays a central role in transposition. We show that the Mu end DNA-binding d omain, I beta gamma, which is responsible for binding the DNA attachme nt sites at each end of the Mu genome, comprises two subdomains, I bet a and I gamma, that are structurally autonomous and do not interact wi th each other in the absence of DNA. The solution structure of the I g amma subdomain has been determined by multidimensional NMR spectroscop y. The structure of I gamma comprises a four helix bundle and, despite the absence of any significant sequence identity, the topology of the first three helices is very similar to that of the homeodomain family of helix-turn-helix DNA-binding proteins. The helix-turn-helix motif of I gamma, however, differs from that of the homeodomains in so far a s the loop is longer and the second helix is shorter, reminiscent of t hat in the POU-specific domain. (C) 1997 Academic Press Limited.