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Mol. Cell. Biol., 07 1997, 3488-3496, Vol 17, No. 7
JD Johnson, W Zhang, A Rudnick, WJ Rutter and MS German
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.
Copyright © 1997, American Society for Microbiology
Transcriptional synergy between LIM-homeodomain proteins and basic helix-loop-helix proteins: the LIM2 domain determines specificity
Hormone Research Institute, Department of Medicine, University of California, San Francisco 94143-0534, USA.
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