The basic helix-loop-helix proteins are dimeric transcription factors that are found in almost all eukaryotes. In animals, they are important regulators of embryonic development, particularly in neurogenesis, myogenesis, heart development and hematopoiesis. deposited research The basic helix-loop-helix (bHLH) proteins form a large superfamily of transcriptional regulators that are found in organisms from yeast to humans and function in critical developmental processes, including sex determination and the development of the nervous system. | Review An overview of the basic helix-loop-helix proteins Susan Jones Address Department of Biochemistry School of Life Sciences University of Sussex Falmer Brighton BN1 9QG UK. E-mail Published 28 May 2004 Genome Biology 2004 5 226 The electronic version of this article is the complete one and can be found online at http 2004 5 6 226 2004 BioMed Central Ltd Abstract The basic helix-loop-helix proteins are dimeric transcription factors that are found in almost all eukaryotes. In animals they are important regulators of embryonic development particularly in neurogenesis myogenesis heart development and hematopoiesis. The basic helix-loop-helix bHLH proteins form a large superfamily of transcriptional regulators that are found in organisms from yeast to humans and function in critical developmental processes including sex determination and the development of the nervous system and muscles. Because of their functional diversity and importance this superfamily has been the subject of a number of recent reviews covering many species 1 2 and also a number of reviews specific to individual species including Saccharomyces cerevisiae 3 Drosophila 4 5 human 6 and Arabidopsis 7-9 . The main emphasis in the recent literature has been on phylogenetic sequence analysis of bHLH families. This article gives an overview of how bHLH proteins are classified by sequence and summarizes their structures and functions. Classifications of bHLH proteins by sequence Members of the bHLH superfamily have two highly conserved and functionally distinct domains which together make up a region of approximately 60 amino-acid residues. At the amino-terminal end of this region is the basic domain which binds the transcription factor to DNA at a consensus hexanucleotide sequence known as the E box. Different families of bHLH proteins recognize different E-box consensus sequences. At the carboxy-terminal end of the region is the HLH domain which facilitates .
