Fig. 2. Structure and possible effects of VP16En. (A) In VP16En, the repressor domain of En (as defined by Han and Manley, 1993) has been removed and replaced by the VP16 transactivating domain. Note that eh2, the domain of En implicated in cooperative binding with Exd, is still present in VP16En. (B) Two possible modes of activation by En. If En activates hh directly or by activating the expression of an intermediate activator (A), VP16En is expected to activate hh expression too. By contrast, if En activates through repression of a repressor, VP16En should activate the expression of this repressor and the net result would be repression of hh expression. (C) Expected effect of VP16En on negative targets of En (such as ci). The expected outcome is the same whether En represses ci expression directly or by repressing an intermediate activator (A').

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