Nuclear factor structure

EPR studies on electron transfer systems where neighboring centers are coupled by spin-spin interactions can yield useful data for analyzing the electron transfer kinetics. In the framework of the Condon approximation, the electron transfer rate constant predicted by electron transfer theories can be expressed as the product of an electronic factor Tab by a nuclear factor that depends explicitly on temperature (258). On the one hand, since iron-sulfur clusters are spatially extended redox centers, the electronic factor strongly depends on how the various sites of the cluster are affected by the variation in the electronic structure between the oxidized and reduced forms. Theoret-... 

A third type of protein involved in subunit assembly is a dimerization cofactor of hepatocyte nuclear factor-la, which selectively stabilizes the dimeric structure of the transcription factor necessary for the binding to DNA.57 Although the transcription factor can dimerize on its own in vitro, in vivo assembly is suggested to be regulated by this tissue-specific 11-kDa cofactor protein.57 ... 

Several papers utilizing 3 mm probe capabilities were also published that delved into the area of protein structures. Hepatocyte nuclear factor 4 was studied by a group lead by Williams.155 It is interesting to note that a 2.7 A X-ray study showed a fatty acid in the pocket of HNF4y. Gas chromatography coupled mass spectrometry (GC/MS) and 3 mm NMR studies of extracts from purified HNF4x led to the identification of mixtures of saturated and crs-monounsaturated Ci4 to Qg fatty acids. Bertini and co-workers156 utilized 3 mm probe capabilities in the determination of the solution structure of CopC, a cupredoxin-like protein involved in copper homeostasis. 

An important eukaryotic transcription factor is the nuclear factor, NF-kB (NF-xB). This factor binds to DNA through i-sheets. The i-sheets of the dimeric transcription factor wrap around the DNA like a mantle. Contacts are made, as in the case of a-helices, with die major groove of the DNA. The structure is shown in Plate 18. 

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