A NEW APPROACH TO THE ANALYSIS OF DNASE I FOOTPRINTING DATA AND ITS APPLICATION TO THE TFIIIA/5S DNA COMPLEX

We have re-examined DNase I footprinting data for the binding of transcription factor IIIA (TFIIIA) to the 5S RNA gene, taking into account the protein-DNA contacts observed in the crystal structure of the DNase I/DNA complex (1, 2). This structure was not available when many of the original footprinting experiments on the TFIIIA/DNA complex were performed. In this way the pattern of DNase I cleavage can be interpreted to map out with greater precision the regions on the 5S DNA occupied by TFIIIA. Then, assuming the binding site for a zinc-finger may be the same as that found in the structure of the zinc-finger protein Zif268/DNA complex (3), and taking into account footprinting data for truncated forms of TFIIIA, the TFIIIA zinc-fingers were fitted within the permitted regions. On the basis of this, an alignment of the zinc-fingers of TFIIIA with its DNA binding site is proposed, which combines features of earlier models (4).