Described are recombinant DNA molecules comprising the regulatory sequence(s) of an intron of the Endothelial Growth Factor (VEGF) receptor-2 gene (Flk-1) or of a gene homologous to the Flk-1 gene, being capable of conferring expression of a heterologous DNA sequence in endothelial cells, preferably in vivo. Vectors comprising said DNA molecules as well as host cells containing the same are provided. Also provided are pharmaceutical and diagnostic compositions comprising such recombinant DNA molecules and vectors. Furthermore, cells and transgenic non-human animals, comprising the aforementioned recombinant DNA molecules or vectors stably integrated into their genome and their use for the identification of substances capable of suppressing or activating transcription of a gene in endothelial cells are described. Described is further the use of the before described recombinant DNA molecules and vectors for the preparation of pharmaceutical compositions for treating, preventing, and/or delaying a vascular or tumorous disease in a subject. Furthermore, uses of the recombinant DNA molecules and vectors of the invention for the preparation of pharmaceutical compositions for inducing a vascular or tumorous disease in a non-human animal are provided.