The human growth hormone locus control region mediates long-distance transcriptional activation independent of nuclear matrix attachment regions

Expression of the human growth hormone (hGH-N) transgene in the mouse pitui tary is dependent on a multicomponent locus control region (LCR). The prima ry determinant of hGH LCR function maps to the pituitary-specific DNase I h ypersensitive sites (HS) HSI,II, located 15 kb 5' to the hGH-N gene. The me chanism by which HSI,II mediates long-distance activation of the hGH locus remains undefined. Matrix attachment regions (MARs) comprise a set of AT-ri ch DNA elements postulated to interact with the nuclear scaffold and to med iate long-distance interactions between LCR elements and their target promo ters. Consistent with this model, sequence analysis strongly predicted a MA R determinant in close proximity to HSI,II. Surprisingly, cell-based analys is of nuclear scaffolds failed to confirm a MAR at this site, and extensive mapping demonstrated that the entire 87 kb region encompassing the hGH LCR and contiguous hGH gene cluster was devoid of MAR activity. Homology searc hes revealed that the predicted MAR reflected the recent insertion of a LIN E 3'-UTR segment adjacent to HSI,II. These data point out discordance betwe en sequence-based MAR predictions and in vivo MAR function and predict a no vel MAR-independent mechanism for long-distance activation of hGH-N gene ex pression.