Using altered specificity Oct-1 and Oct-2 mutants to analyze the regulation of immunoglobulin gene transcription.
Oct-1 and Oct-2 represent the prototypical example of related transcription factors with identical DNA recognition properties. They bind functionally critical octamer elements found in diverse regulatory sequences. It has not been possible to determine directly if these factors are functionally redundant or selective when interacting with different regulatory sequences in the appropriate cell type. An equivalent pair of altered DNA-binding specificity mutants of Oct-1 and Oct-2 are used to examine their function from varied regulatory contexts in B cells. These factors function as redundant activators of immunoglobulin (Ig) gene promoters (Vkappa and VH) and a histone H2B promoter. The structural basis of redundancy resides in the highly conserved DNA-binding POU domain, because this domain of either protein can activate transcription from both Ig and H2B promoters. We find that the nature of a distal enhancer dictates the relative potency of Oct-1 versus Oct-2 bound to a promoter. Oct-1 preferentially stimulates transcription from a VH or Vkappa promoter in combination with enhancers from the IgH or Igkappa locus, respectively. In this context, the more potent action of Oct-1 is dependent on a region external to the POU domain. These results suggest that Oct-1 may be the critical regulator of Ig gene transcription during B cell development and provide an explanation for selective Ig isotype expression defects in Oct-2 and OCA-B null mice.
Shah
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PC
Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
Bertolino
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E
Singh
H
H
D000818:Animals; D001402:B-Lymphocytes; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D005803:Genes, Immunoglobulin; D006657:Histones / Q000235:genetics; D051863:Host Cell Factor C1; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics; D007145:Immunoglobulin kappa-Chains / Q000235:genetics; D051379:Mice; D008817:Mice, Mutant Strains; D009154:Mutation; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D050809:POU Domain Factors; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000235:genetics; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; C497693:Hcfc1 protein, mouse; D006657:Histones; D051863:Host Cell Factor C1; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D007145:Immunoglobulin kappa-Chains; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D050809:POU Domain Factors; C490424:Pou2af1 protein, mouse; C494166:Pou2f1 protein, mouse; C489206:Pou2f2 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors