The differentiation of muscle cells from the somites (segments of mesoderm) of a developing embryo is controlled by myogenin, an helix-loop-helix gene regulatory protein that functions as a heterodimer with another member of the MyoD family of HLH proteins (see Figure A below). The activity of myogenin must be carefully controlled to prevent it from triggering premature expression of the muscle program of cell differentiation. The myogenin gene is turned on in advance of the time when it is needed, but myogenin is prevented from functioning by phosphorylation of its DNA-binding domain and by tight binding to
Id, an HLH protein that lacks a DNA-binding domain (see Figure B below). Explain how dimerization with Id and phosphorylation of the DNA-binding domain might act to keep myogenin nonfunctional. (2 pts)
The differentiation of muscle cells from the somites (segments of mesoderm) of a developing embryo is controlled by myogenin, an helix-loop-helix gene regulatory protein that functions as a heterodimer with another member of the MyoD family of HLH proteins (see Figure A below). The activity of myogenin must be carefully controlled to prevent it from triggering premature expression of the muscle program of cell differentiation. The myogenin gene is turned on in advance of the time when it is needed, but myogenin is prevented from functioning by phosphorylation of its DNA-binding domain and by tight binding to
Id, an HLH protein that lacks a DNA-binding domain (see Figure B below). Explain how dimerization with Id and phosphorylation of the DNA-binding domain might act to keep myogenin nonfunctional. (2 pts)
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