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A dominant chromatin‐opening activity in 5′ hypersensitive site 3 of the human beta‐globin locus control region.
Author(s) -
Ellis J.,
TanUn K. C.,
Harper A.,
Michalovich D.,
Yannoutsos N.,
Philipsen S.,
Grosveld F.
Publication year - 1996
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1996.tb00388.x
Subject(s) - locus control region , biology , hypersensitive site , chromatin , globin , dnase i hypersensitive site , microbiology and biotechnology , enhancer , transgene , locus (genetics) , deoxyribonuclease i , regulatory sequence , gene , genetics , promoter , gene expression , base sequence
Single‐copy human beta‐globin transgenes are very susceptible to suppression by position effects of surrounding closed chromatin. However, these position effects are overcome by a 20 kbp DNA fragment containing the locus control region (LCR). Here we show that the 6.5 kbp microlocus LCR cassette reproducibly directs full expression from independent single‐copy beta‐globin transgenes. By testing individual DNase I‐hypersensitive sites (HS) present in the microlocus cassette, we demonstrate that the 1.5 kbp 5′HS2 enhancer fragment does not direct beta‐globin expression from single‐copy transgenes. In contrast, the 1.9 kbp 5′HS3 fragment directs beta‐globin expression in five independent single‐copy transgenic mouse lines. Moreover, the 5′HS3 core element and beta‐globin proximal promoter sequences are DNase I hypersensitive in fetal liver nuclei of these expressing transgenic lines. Taken together, these results demonstrate that LCR activity is the culmination of at least two separable functions including: (i) a novel activity located in 5′HS3 that dominantly opens and remodels chromatin structure; and (ii) a recessive enhancer activity residing in 5′HS2. We postulate that the different elements of the LCR form a ‘holocomplex’ that interacts with the individual globin genes.