The B cell coactivator Bob1 shows DNA sequence-dependent complex formation with Oct-1/Oct-2 factors, leading to differential promoter activation.
We have shown previously that both octamer binding transcription factors, namely the ubiquitous Oct-1 and the B cell-specific Oct-2A protein, can be enhanced in transcriptional activity by their association with the B cell-specific coactivator protein Bob1, also called OBF-1 or OCA-B. Here we study the structural requirements for ternary complex formation of DNA-Oct-Bob1 and coactivation function of Bob1. In analogy to DNA-bound transcription factors, Bob1 has a modular structure that includes an interaction domain (amino acids 1-65) and a C-terminal domain (amino acids 65-256), both important for transcriptional activation. A mutational analysis has resolved a region of seven amino acids (amino acids 26-32) in the N-terminus of Bob1 that are important for contacting the DNA binding POU domain of Oct-1 or Oct-2. In contrast to the viral coactivator VP16 (vmw65), which interacts with Oct-1 via the POU homeosubdomain, Bob1 association with Oct factors requires residues located in the POU-specific subdomain. Because the same residues are also involved in DNA recognition, we surmised that this association would affect the DNA binding specificity of the Oct-Bob1 complex compared with free Oct factors. While Oct-1 or Oct-2 bind to a large variety of octamer sequences, Bob1 ternary complex formation is indeed highly selective and occurs only in a subset of these sequences, leading to the differential coactivation of octamer-containing promoters. The results uncover a new level in selectivity that furthers our understanding in the regulation of cell type-specific gene expression.
Gstaiger
M
M
Institute of Molecular Biology II, University of Zürich, Switzerland.
Georgiev
O
O
van Leeuwen
H
H
van der Vliet
P
P
Schaffner
W
W
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000502:physiology*; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D006367:HeLa Cells / Q000378:metabolism; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics; D018398:Homeodomain Proteins / Q000378:metabolism*; D051863:Host Cell Factor C1; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; C497692:HCFC1 protein, human; D017405:Herpes Simplex Virus Protein Vmw65; D018398:Homeodomain Proteins; D051863:Host Cell Factor C1; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; C091546:POU2AF1 protein, human; C494165:POU2F1 protein, human; C058435:POU2F2 protein, human; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors