A deletion of the human beta-globin locus activation region causes a major alteration in chromatin structure and replication across the entire beta-globin locus.
Naturally occurring deletions that remove sequences located approximately 60 kb upstream of the human adult beta-globin gene result in the failure to transcriptionally activate the cis-linked globin genes in erythroid cells. In addition, transfection, transgenic, and somatic cell hybrid studies have revealed that sequences within this region are essential for the developmentally regulated high-level expression of cis-linked globin genes. This regulatory region located at the 5' end of the beta-globin locus has been termed the locus activation region (LAR). Using somatic cell hybrids, we have studied the chromatin structure and timing of DNA replication of the normal human beta-globin locus and a locus containing a de novo 25-kb deletion that removes elements of the LAR. As a result of this deletion, the entire beta-globin locus and sequences approximately 100 kb 5' and 3' of the adult beta-globin gene are DNase I-resistant and do not form characteristic distant hypersensitive sites. These sequences also replicate late in S phase in an erythroid cell background. In contrast, the sequences of the normal locus are DNase I sensitive and early replicating. These results suggest that the LAR is required for both the erythroid-specific chromatin structure and timing of DNA replication over a large physical distance.
Forrester
W C
WC
Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
Epner
E
E
Driscoll
M C
MC
Enver
T
T
Brice
M
M
Papayannopoulou
T
T
Groudine
M
M
D002843:Chromatin / Q000737:chemistry*; D002872:Chromosome Deletion; D002874:Chromosome Mapping; D004261:DNA Replication / Q000235:genetics*; D015870:Gene Expression / Q000502:physiology; D005914:Globins / Q000235:genetics*; D006801:Humans; D006822:Hybrid Cells; D013789:Thalassemia / Q000235:genetics
D002843:Chromatin; D005914:Globins