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The A/B domains of nuclear receptors such as thyroid receptor α (TRα) are considered to be conformationally flexible and can potentially adopt multiple structural conformations. We used intrinsic tryptophan fluorescence quenching and circular dichroism spectroscopy to characterize the unfolding of this A/B domain upon DNA binding to the contiguous DNAbinding domain (DBD). We propose that this allosteric change in A/B domain conformation can allow it to make the multiple interactions with distinct molecular factors of the transcriptional preinitiation complex. We further suggest that by influencing the affinity of the DBD for DNA, A/B domain can fine-tune the recognition of promotor DNA by TRα. [ABSTRACT FROM AUTHOR]

The germ cell nuclear factor (GCNF) is a nuclear orphan receptor and a putative regulator of the pluripotent state of cells. Although it was first described in mouse germ cells, GCNF is also expressed in mouse and Xenopus embryos. By means of 5′RACE we have identified a novel isoform of Xenopus laevis GCNF that is predominantly expressed in germ cells, whereas both the oocyte and embryonic forms are expressed during Xenopus embryogenesis. EST database search revealed that the homologues of both isoforms are also transcribed in Xenopus tropicalis. [Copyright &y& Elsevier]