Dual promoter activation by the human beta-globin locus control region.
The human beta-globin locus control region (LCR) is necessary for high-level and position-independent expression of globin genes in erythroid cells. A variety of mechanisms have been proposed for the cis-activation of individual members of the beta-globin gene family by the LCR located 10-50 kilobases upstream. It is not known, however, whether a given LCR can activate all developmentally appropriate globin family members on its chromosome or whether, within a given chromosome, the LCR must be committed to activating only a single gene. We have devised an experiment to distinguish between these possibilities. This experiment takes advantage of the fact that if two genes in a cluster are transcriptionally active and their promoters, therefore, are in a conformation hypersensitive to nucleases, restriction enzymes that cleave the promoters will excise the intervening chromatin fragment. The Apa I sites on human fetal G gamma- and A gamma-globin gene promoters are accessible to cleavage in nuclei from the human erythroleukemia cell line K562, which expresses these genes, but not in HeLa cells. We find that Apa I digestion leads to excision in high yield of the fragment spanning these promoters, showing that a LCR element is capable of sharing its activating function among members of a gene cluster on a single chromosome.
Bresnick
E H
EH
National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Laboratory of Molecular Biology, Bethesda, MD 20892.
Felsenfeld
G
G
D002478:Cells, Cultured; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism; D002877:Chromosomes, Human; D004273:DNA, Neoplasm / Q000187:drug effects; D015252:Deoxyribonucleases, Type II Site-Specific / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D005914:Globins / Q000096:biosynthesis / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*
D002843:Chromatin; D004273:DNA, Neoplasm; D005914:Globins; D015252:Deoxyribonucleases, Type II Site-Specific; C038485:GGGCCC-specific type II deoxyribonucleases