β-Galactosidase activity and CREB/ELF-1 binding assays. (A) β-Galactosidase activity of protein extracts from various organs of the Hprt-targeted mice. Data represent mean ± SE of 4 replicates. *P < .05; **P < .01; **P < .001. n.s., not significant. (B-C) ChIP assay was performed using mouse heart endothelial cells from Hprt-targeted mice carrying a mutation of the CRE site (CREm) or −52 ETS site (−52ETSm). The sheared DNA samples were analyzed by 1.7% agarose gel. Resulting DNA-protein complexes were immunoprecipitated in the absence or presence antibodies to ELF-1 or CREB. Real-time PCR analysis was performed using the precipitated DNA fragments and primers for the human proximal promoter and LacZ cDNA (C).