The beta-globin locus control region (LCR) is a powerful regulatory element required for high-level globin gene expression. We have generated transgenic mouse lines carrying a beta-globin locus yeast artificial chromosome lacking the LCR to determine if the LCR is required for globin gene activation. beta-Globin gene expression was analyzed by RNase protection, but no detectable levels of epsilon-, gamma- and beta-globin gene transcripts were produced at any stage of development. These findings suggest that the presence of the LCR is a minimum requirement for globin gene expression. Next, we tested whether the LCR is necessary to activate globin gene expression in a gamma-globin promoter mutant that causes hereditary persistence of fetal hemoglobin (HPFH). beta-YAC transgenic mice carrying the -117 HPFH mutation and a HS3 core deletion that specifically abolishes gamma-globin gene expression during definitive erythropoiesis were produced to test whether the -117 (A)gamma promoter is activated in the absence of interaction with the LCR. In four transgenic mouse lines, gamma-globin gene expression was absent in adult erythrocytes, suggesting that an interaction between the gamma-globin gene promoter and the LCR is required for gamma gene activation even when the promoter contains an HPFH mutation.