title: Identification of a highly conserved module in E proteins required for in vivo helix-loop-helix dimerization.
abstract: Basic helix-loop-helix (bHLH) transcription factors often function as heterodimeric complexes consisting of a tissue-specific factor such as SCL/tal or MyoD bound to a broadly expressed E protein. bHLH dimerization therefore appears to represent a key regulatory step in cell lineage determination and oncogenesis. Previous functional and structural studies have indicated that the well defined HLH domain is both necessary and sufficient for dimerization. Most of these studies, however, have employed in vitro systems for analysis of HLH dimerization, and their implications for the requirements for in vivo dimerization remain unclear. Using multiple approaches, we have analyzed bHLH dimerization in intact, living cells and have identified a novel domain in E proteins, domain C, which is required for in vivo dimerization. Domain C, which lies just carboxyl-terminal to helix 2 of the HLH domain, represents the most highly conserved region within E proteins and appears to influence the in vivo conformation of the adjacent HLH domain. These results suggest that HLH dimerization in vivo may represent a complex, regulated process that is distinct from HLH dimerization in vitro.
authors.affiliation: Institute of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4943, USA. ang@po.cwru.edu
authors.forename: A N
authors.initials: AN
authors.lastname: Goldfarb
authors.forename: K
authors.initials: K
authors.lastname: Lewandowska
authors.forename: C A
authors.initials: CA
authors.lastname: Pennell
mesh_terms: D000595:Amino Acid Sequence; D051792:Basic Helix-Loop-Helix Proteins; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D019143:Evolution, Molecular; D018257:Helix-Loop-Helix Motifs; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D011485:Protein Binding; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D058125:Transcription Factor 7-Like 1 Protein; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000145:classification
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D017570:MyoD Protein; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D051820:TCF Transcription Factors; D015534:Trans-Activators; D058125:Transcription Factor 7-Like 1 Protein; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; C544912:TCF7L1 protein, human; C544894:TCF7L2 protein, human; C073366:TCF12 protein, human