1Yen Choo and John W. R. Schwabe are at the Medical Research Council Laboratory of Molecular Biology, Hills Road Cambridge CB2 2QH, UK.
2email: choo@mrc-lmb.cam.ac.uk
3email: jwsr@mrc-lmb.cam.ac.uk
How is it possible that nine small repeated 'zinc finger' units (each spanning just 3 or 4 base pairs) can protect the whole 50 base pair binding site of TFIIIA and why should such a periodic protein structure give rise to such an asymmetric footprint on DNA? The crystal structure of the first six fingers of TFIIIA bound to 31 base pairs of DNA explains everything: not all zinc fingers act alike.
