title: Transcriptional synergy between LIM-homeodomain proteins and basic helix-loop-helix proteins: the LIM2 domain determines specificity.
abstract: LIM-homeodomain proteins direct cellular differentiation by activating transcription of cell-type-specific genes, but this activation requires cooperation with other nuclear factors. The LIM-homeodomain protein Lmx1 cooperates with the basic helix-loop-helix (bHLH) protein E47/Pan-1 to activate the insulin promoter in transfected fibroblasts. In this study, we show that two proteins originally called Lmx1 are the closely related products of two distinct vertebrate genes, Lmx1.1 and Lmx1.2. We have used yeast genetic systems to delineate the functional domains of the Lmx1 proteins and to characterize the physical interactions between Lmx1 proteins and E47/Pan-1 that produce synergistic transcriptional activation. The LIM domains of the Lmx1 proteins, and particularly the second LIM domain, mediate both specific physical interactions and transcriptional synergy with E47/Pan-1. The LIM domains of the LIM-homeodomain protein Isl-1, which cannot mediate transcriptional synergy with E47/Pan-1, do not interact with E47/Pan-1. In vitro studies demonstrate that the Lmx1.1 LIM2 domain interacts specifically with the bHLH domain of E47/Pan-1. These studies provide the basis for a model of the assembly of LIM-homeodomain-containing complexes on DNA elements that direct cell-type-restricted transcription in differentiated tissues.
authors.affiliation: Hormone Research Institute, Department of Medicine, University of California, San Francisco 94143-0534, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Johnson
authors.forename: W
authors.initials: W
authors.lastname: Zhang
authors.forename: A
authors.initials: A
authors.lastname: Rudnick
authors.forename: W J
authors.initials: WJ
authors.lastname: Rutter
authors.forename: M S
authors.initials: MS
authors.lastname: German
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000502:physiology; D005786:Gene Expression Regulation; D018257:Helix-Loop-Helix Motifs; D018398:Homeodomain Proteins / Q000502:physiology*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D051820:TCF Transcription Factors; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D051820:TCF Transcription Factors; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors