Myodes

Figure 10.24 Structure of a monomer of the DNA-binding domain of the transcription factor MyoD. The domain, which belongs to the b/HLH family, comprises two a helices joined by a loop region. The basic region (blue) and the first helix HI (red) of the helix-loop-helLx region form one continous a helix. (Adapted from P.C.M. Ma et al.. Cell 77 451-459, 1994.)...

Figure 10.25 Structure of the dimerization region of MyoD. The a helices HI (red and brown) and H2 (light and dark green) of the two monomers form a four-helix bundle that keeps the dimer together. The loops (yellow and orange) are on the outside of the four-helix bundle. (Adapted from P.C.M. Ma et al.. Cell 77 4S1-4S9, 1994.)...

Figure 10.27 5equence-speclfic contacts between DNA and one monomer of MyoD. 

Figure 10.28 Schematic diagram of the binding of the transcription factor Max to DNA. The two monomers of Max (blue and green) form a dimer through both the helix-loop-helLx regions which form a four-helix bundle like MyoD, and the zipper regions, which are arranged in a coiled coil. The N-terminal basic regions bind to DNA in a way similar to GCN4 and MyoD. (Adapted from A.R. Ferre-D Amare et al., Nature 363 38-4S, 1993.)...

Max and MyoD recognize the DNA HLH consensus sequence by different specific protein-DNA interactions... 

The helical basic region of Max binds to the major groove of DNA in the same manner as MyoD (see Figures 10.26 and 10.28). The DNA structure is essentially that of B-DNA with minor distortions as in the MyoD complex. Both Max and MyoD recognize the same consensus half-site DNA sequence 5 -CAC-3 ... 

Three residues. His 28, Glu 32 and Arg 36, form specific interactions with the edges of the bases in the major groove of DNA. Like MyoD, a Glu residue recognizes the first two bases, C and A, of the recognition sequence. 

Connolly, B., Trenholme, K. and Smith, D.F. (1996) Molecular cloning of a myoD-like gene from the parasitic nematode, Trichinella spiralis. Molecular and Biochemical Parasitology 81, 137—149. 

Halevy, O., Novitch, B.G., Spicer, D.B., Skapek, S.X., Rhee, J., Hannon, G.J., Beach, D. and Lassar, A.B. (1995) Correlation of terminal cell cycle arrest of skeletal muscle with induction of p21 by MyoD. Science 267, 1018-1021. 

To analyze the role of the N-terminal residue of MyoD as a ubiquitination site, we fused to WT MyoD, upstream to the N-terminal residue, a 6 x Myc tag, and monitored the stability of the tagged protein. We showed that it is stable both in vitro and in vivo. It should be noted that the two first N-terminal residues of the Myc tag, methionine and glutamate, are identical to the first two N-terminal residues in MyoD. In addition, the Myc tag also contains a lysine residue. Thus, altogether, six additional lysine residues were added to WT MyoD in addition to its own nine native residues. Nevertheless, the tag stabilizes it, probably by blocking access to a specific N-terminal residue, and, as became clear later (see below), to its neighboring domain. 

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