CHARACTERIZATION OF DEOXYRIBONUCLEIC-ACID PROTEIN INTERACTIONS AT A GROWTH HORMONE-INDUCIBLE NUCLEASE HYPERSENSITIVE SITE IN THE RAT INSULIN-LIKE GROWTH-FACTOR-I GENE

Many of the growth-promoting effects of GH are mediated by insulin-lik e growth factor-I (IGF-I), a highly conserved, 70-residue basic peptid e. Previous studies have demonstrated that GH rapidly stimulates IGF-I expression in vivo, and our laboratory has identified a GK-regulated alteration in chromatin configuration, manifested as a hormonally indu ced deoxyribonuclease-I (DNase-I)-hypersensitive site in the second IG F-I intron. In the current study, we have used in vivo DNase-I footpri nting to map this hormonally responsive chromatin domain to an approxi mately 350-nucleotide region and have identified DNA-protein interacti ons within the hypersensitive site by in vitro gel mobility shift expe riments and DNase-I footprinting studies. DNA-protein binding was loca lized to two adjacent segments of 32 and 48 nucleotides. In 1 of these regions, protein-DNA contacts were also detected in vivo on guanine r esidues by dimethylsulfate footprinting. DNA-binding activity was pres ent in GH-deficient rats, but was not modified by hormone treatment. O ur results define a rapid and reversible genomic alteration in respons e to GH in a GH-regulated gene and delineate a target within chromatin for GH action.