Topology of recombinant rat upstream binding factor

Transmission electron microscopy and single particle electron crystallograp hy were employed to reconstruct high-quality projection images of a recombi nant, acidic tail deficient form of rat upstream binding factor. The upstre am binding factor was found to be dimeric and approximately 10 nm in diamet er with a central region of low density. Distinct nodes were observable, of size and spacing consistent with being HMG boxes 3 and 4. The dimerisation domain seemed most probably to be located in the internal region of the st ructure.