These studies allow us to establish the binding stoichiometry and to draw conclusions about the nature of the calmodulin-HLHmp interactions from the observed spectral changes. For example, we hope to establish whether the interaction of calmodulin with bHLH is similar to that of calmodulin with peptides from calmodulin-interacting protein kinases or whether another part of the calmodulin surface is involved. The Isl-1 gene in rat codes for a 42 KDa protein that specifically binds to a transcription activating domain of the insulin gene. The homeodomain is thought to mediate DNA binding while the LIM domain may be involved in regulation of the protein. Efficient expression systems and purification protocols for both domains have been developed.
CD spectroscopy indicate that the homeodomain has a significant content of a-helical structure.
A significant stabilization of the protein structure is observed by thermal and chemical denaturation, as demonstrated by CD-spectroscopy. NMR data has been recorded. These show that a structural determination by NMR should be possible, and such a study is now undertaken. Four-Way Junctions Branched DNA species are commonly postulated as intermediates in DNA rearrangements. Enzymes must interact specifically with the DNA structure to bring about the recombination event.