A dominant chromatin-opening activity in 5' hypersensitive site 3 of the human beta-globin locus control region.
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.
Ellis
J
J
Department of Genetics, Research Institute, Hospital for Sick Children,Toronto, Canada
Tan-Un
K C
KC
Harper
A
A
Michalovich
D
D
Yannoutsos
N
N
Philipsen
S
S
Grosveld
F
F
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002843:Chromatin / Q000235:genetics*; D002874:Chromosome Mapping; D017931:DNA Primers / Q000235:genetics; D003850:Deoxyribonuclease I; D004742:Enhancer Elements, Genetic; D005260:Female; D015870:Gene Expression; D005914:Globins / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D008957:Models, Genetic; D008969:Molecular Sequence Data
D002843:Chromatin; D017931:DNA Primers; D005914:Globins; D003850:Deoxyribonuclease I