Concerted repression of an immunoglobulin heavy-chain enhancer, 3' alpha E(hs1,2).
The transcription factor, B-cell-specific activator protein (BSAP), represses the murine immunoglobulin heavy-chain 3' enhancer 3' alpha E(hs1,2) in B cells. Analysis of various 3'alpha E deletional constructs indicates that sequences flanking a and b BSAP-binding sites are essential for appropriate regulation of the enhancer. An octamer motif 5' of the a site and a specific G-rich motif 3' of the b site were identified by competition in electrophoretic mobility-shift assays and methylation-interference foot-printing analysis. Site-directed mutagenesis of either the octamer or G-rich sites resulted in the complete release of repression of 3' alpha E(hs1,2), implicating these two motifs in the repression of this enhancer in B cells. However, when both BSAP-binding sites were mutated, the octamer and G-rich motifs functioned as activators. Moreover, in plasma cells, when BSAP is not expressed, 3' alpha E(hs1,2) is active, and its activity depends on the presence of the other two factors. These results suggest that in B cells, 3' alpha E (hs1,2) is down-regulated by the concerted actions of BSAP, octamer, and G-rich DNA-binding proteins. Supporting this notion of concerted repression, a physical interaction between BSAP and octamer-binding proteins was demonstrated using glutathione S-transferase fusion proteins. Thus, concerted repression of 3' alpha E (hs1,2) in B cells provides a sensitive mechanism by which this enhancer, either individually or as part of a locus-controlling region, is highly responsive to any of several participating factors.
Singh
M
M
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Birshtein
B K
BK
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D001665:Binding Sites; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D005803:Genes, Immunoglobulin; D018398:Homeodomain Proteins / Q000378:metabolism; D051863:Host Cell Factor C1; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000378:metabolism*; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D009838:Oligodeoxyribonucleotides; D051757:PAX5 Transcription Factor; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; C497693:Hcfc1 protein, mouse; D018398:Homeodomain Proteins; D051863:Host Cell Factor C1; D007143:Immunoglobulin Heavy Chains; D009687:Nuclear Proteins; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D009838:Oligodeoxyribonucleotides; D051757:PAX5 Transcription Factor; C497282:Pax5 protein, mouse; C494166:Pou2f1 protein, mouse; C489206:Pou2f2 protein, mouse; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D015500:Chloramphenicol O-Acetyltransferase