The Ets site (bp 308) is required for the endothelium specificity of the

Flk-1 minimal enhancer. (A) DNAseI footprint. The 430-bp Flk-1 minimal enhancer subcloned into pBluescript KS was incubated with increasing amounts (triangles) of BSA or nuclear extracts from BAE or TK1 cells, and digested with DNAseI. The cleavage products were analyzed as described in “Materials and methods” on a sequencing gel. Sequencing reactions terminated at the indicated bases were loaded in parallel. The position of the Ets site (bp 308) of the minimal enhancer is indicated. Arrows indicate changes in the DNAseI cleaving pattern. HS indicates DNAseI hypersensitive site. (B,C) Different LacZ-stained mouse embryos transgenic for a construct containing the 939-bp Flk-1 promoter and the 430-bp minimal enhancer with a mutation in the Ets site at bp 308. (D) LacZ expression in a mouse embryo transgenic for a construct containing the 939-bpFlk-1 promoter and the 430-bp minimal enhancer with a mutation in the Ets site at bp 260.