FIG. 1.

Identification of cis-acting elements in the mouse flk1 first-intronic enhancer. (A) Scheme of mouse flk1 genomic locus and transgenic construct. A total of 940 bp (positions from −640 to +299) of the 5′-flanking sequence of the mouse flk1 gene and 510 bp of the first intronic enhancer are sufficient to target lacZ expression to the vascular endothelium in transgenic mice. (B) Diagram of the general approach undertaken to identify cis-acting elements in the mouse flk1 first intronic enhancer. (C) Protein-binding site identification by in vitro DNase I footprinting. A single footprint, located between bp 150 and 195 in the intronic enhancer, was detected on both sense and antisense strands. The dark line denotes the putative binding site for DNA-binding proteins. (D) Analysis of cell type differences in DNase I footprinting patterns. The labeled probe was incubated with nuclear extracts from MECs, Py-4-1, C166, bEnd.3, and C2C12 cells, or BSA prior to digestion with DNase I.