The diversity of transcription factor-DNA complexes reviewed in this paper marks the extent of discovery since the first transcription factor-DNA co-crystal structures appeared less than ten years ago. The DNA-binding domains of transcription factors were classified into families, many of which have been identified by comparative amino acid sequence analysis. The three-dimensional views of their respective families revealed new designs as well as unanticipated similarities to older ones. Several hoped-for simplicities in their DNA-recognition mechanism have proved illusory, but other unexpected regularities have emerged.
Four symmetries, which are needed for the determination of a diffraction group by convergent-beam electron diffraction (CBED), were obtained from one selected-area CBED pattern. An inversion symmetry and a four-fold inversion symmetry were observed by selectedarea CBED technique. Coherent CBED patterns show the phase information of crystal structure factors. The phase relations between crystal structure factors for a non-mirror symmetry, a mirror symmetry and a glide symmetry were observed by coherent CBED.
The transition to a symmetric ice has been observed at about 60 GPa by infrared absorption spectroscopy. The hydrogen-bond symmetrization, which is accompanied by a subsequent deformation of the hydrogen-bond potential from a double to single minimum shape, is well recognized as a turn in the pressure dependence of the OH stretching frequencies from a decrease to increase at the transition point. In the intermediate state, the stretching vibrational modes is shown to form a continuous energy band as a result of quantum-mechanical manybody effects. This effect leads to an interference phenomenum between the proton-related vibrational states.