Targeted recruitment of histone acetyltransferase activity to a locus control region

Locus control regions (LCRs) are capable of activating target genes over su bstantial distances and establishing autonomously regulated chromatin domai ns. The basis for this action is poorly defined. Human growth hormone gene (hGH-N) expression is activated by an LCR marked by a series of DNase I-hyp ersensitive sites (HSI-III and HSV) in pituitary chromatin, These HSs are l ocated between -15 and -32 kilobases (kb) relative to the hGH transcription start site. To establish a mechanistic basis for hGH LCR function, we carr ied out acetylation mapping of core histones H3 and H4 in chromatin encompa ssing the hGH cluster. These studies revealed that the entire LCR was selec tively enriched for acetylation in chromatin isolated from a human pituitar y somatotrope adenoma and in pituitaries of mice transgenic for the hGH loc us, but not in hepatic or erythroid cells. Quantification of histone modifi cation in the pituitary revealed a dramatic peak at HSI/II, the major pitui tary-specific hGH LCR determinant (-15 kb), with gradually decreasing level s of modification extending from this site in both 5'- and 3'-directions. T he 5'-border of the acetylated domain coincided with the 5' most hGH LCR el ement, HSV (-34 kb); and the 3'-border included the expressed hGH-N gene, b ut did not extend farther 3' into the placenta-specific region of the gene cluster. These data support a model of LCR function involving targeted recr uitment and subsequent spreading of histone acetyltransferase activity to e ncompass and activate a remote target gene.