genetics assignment (2)

In figure 2 (attached) the authors see that CBEPa can repress the expression of a plasmid that contains the promoter sequence for slow MyHC2 fused to luciferase, but that CBEPb is not so effective at doing so. Taken at face value, this experiment would indicate that alpha represses the expression of the slow MyHC2, but beta doesn't. But there could be a number of reasons why the result may be misleading. Letting aside human errors, what do you think might be alternative explanations for the observed results? And what experiments would you set up to try and see if your hypotheses might be correct ? (provide an overall experimental approach, no need for a ton of detail).(500 words)