Decoding hematopoietic specificity in the helix-loop-helix domain of the transcription factor SCL/Tal-1

Mol Cell Biol. 2004 Sep;24(17):7491-502. doi: 10.1128/MCB.24.17.7491-7502.2004.


The helix-loop-helix (HLH) domain is employed by many transcription factors that control cell fate choice in multiple developmental settings. Previously, we demonstrated that the HLH domain of the class II basic HLH (bHLH) protein SCL/Tal-1 is critical for hematopoietic specification. We have now identified residues in this domain that are essential for restoring hematopoietic development to SCL-/- embryonic stem cells and sufficient to convert a muscle-specific HLH domain to one able to rescue hematopoiesis. Most of these critical residues are distributed in the loop of SCL, with one in helix 2. This is in contrast to the case for MyoD, the prototype of class II bHLH proteins, where the loop seems to serve mainly as a linker between the two helices. Among the identified residues, some promote heterodimerization with the bHLH partners of SCL (E12/E47), while others, unimportant for this property, are still crucial for the biological function of SCL. Importantly, the residue in helix 2 specifically promotes interaction with a known partner of SCL, the LIM-only protein LMO2, a finding that strengthens genetic evidence that these proteins interact. Our data highlight the functional complexity of bHLH proteins, provide mechanistic insight into SCL function, and strongly support the existence of an active SCL/LMO2-containing multiprotein complex in early hematopoietic cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Amino Acid Sequence
  • Animals
  • Basic Helix-Loop-Helix Transcription Factors
  • Cell Line
  • Cell Lineage
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Helix-Loop-Helix Motifs*
  • Hematopoiesis / genetics*
  • Hematopoiesis / physiology
  • LIM Domain Proteins
  • Macromolecular Substances
  • Metalloproteins / genetics
  • Metalloproteins / metabolism
  • Mice
  • Mice, Knockout
  • Molecular Sequence Data
  • Multiprotein Complexes
  • Mutation
  • Phenylalanine / metabolism
  • Protein Binding
  • Proto-Oncogene Proteins / chemistry
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Sequence Alignment
  • Stem Cells / physiology*
  • T-Cell Acute Lymphocytic Leukemia Protein 1
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • Adaptor Proteins, Signal Transducing
  • Basic Helix-Loop-Helix Transcription Factors
  • DNA-Binding Proteins
  • LIM Domain Proteins
  • Lmo2 protein, mouse
  • Macromolecular Substances
  • Metalloproteins
  • Multiprotein Complexes
  • Proto-Oncogene Proteins
  • T-Cell Acute Lymphocytic Leukemia Protein 1
  • Tal1 protein, mouse
  • Transcription Factors
  • Phenylalanine