PlantTFDB
PlantRegMap/PlantTFDB v5.0
Plant Transcription Factor Database
Previous version: v3.0 v4.0
Trifolium medium
bHLH Family
Species TF ID Description
MCH80863.1bHLH family protein
MCH81008.1bHLH family protein
MCH81196.1bHLH family protein
MCH82153.1bHLH family protein
MCH82846.1bHLH family protein
MCH83550.1bHLH family protein
MCH83648.1bHLH family protein
MCH84445.1bHLH family protein
MCH85141.1bHLH family protein
MCH86056.1bHLH family protein
MCH87223.1bHLH family protein
MCH87302.1bHLH family protein
MCH88086.1bHLH family protein
MCH89216.1bHLH family protein
MCH90625.1bHLH family protein
MCH91655.1bHLH family protein
MCH91830.1bHLH family protein
MCH93362.1bHLH family protein
MCH94818.1bHLH family protein
MCH94829.1bHLH family protein
MCH95454.1bHLH family protein
MCH96536.1bHLH family protein
MCH96725.1bHLH family protein
MCH98333.1bHLH family protein
MCI00271.1bHLH family protein
MCI02042.1bHLH family protein
MCI03616.1bHLH family protein
MCI06284.1bHLH family protein
MCI06835.1bHLH family protein
MCI07360.1bHLH family protein
MCI07561.1bHLH family protein
MCI08389.1bHLH family protein
MCI08607.1bHLH family protein
MCI08878.1bHLH family protein
MCI08890.1bHLH family protein
MCI12069.1bHLH family protein
MCI13549.1bHLH family protein
MCI14208.1bHLH family protein
MCI15882.1bHLH family protein
MCI17871.1bHLH family protein
MCI18243.1bHLH family protein
MCI20212.1bHLH family protein
MCI21186.1bHLH family protein
MCI25196.1bHLH family protein
MCI26025.1bHLH family protein
MCI30301.1bHLH family protein
MCI37792.1bHLH family protein
MCI40150.1bHLH family protein
MCI44009.1bHLH family protein
MCI46028.1bHLH family protein
MCI49824.1bHLH family protein
bHLH Family Introduction

The basic/helix-loop-helix (bHLH) proteins are a superfamily of transcription factors that have been well characterized in nonplant eukaryotes, especially in mammalian systems, in which considerable structural, functional, and phylogenetic analyses have been performed. The data indicate that bHLH proteins are important regulatory components in transcriptional networks in these systems, controlling a diversity of processes from cell proliferation to cell lineage establishment.

This family is defined by the bHLH signature domain, which consists of 60 amino acids with two functionally distinct regions. The basic region, located at the N-terminal end of the domain, is involved in DNA binding and consists of 15 amino acids with a high number of basic residues. The HLH region, at the C-terminal end, functions as a dimerization domain and is constituted mainly of hydrophobic residues that form two amphipathic -helices separated by a loop region of variable sequence and length. Outside of the conserved bHLH domain, these proteins exhibit considerable sequence divergence. Cocrystal structural analysis has shown that the interaction between the HLH regions of two separate polypeptides leads to the formation of homodimers and/or heterodimers and that the basic region of each partner binds to half of the DNA recognition sequence. Some bHLH proteins form homodimers or restrict their heterodimerization activity to closely related members of the family. On the other hand, some can form heterodimers with one or several different partners.

The core DNA sequence motif recognized by the bHLH proteins is a consensus hexanucleotide sequence known as the E-box (5'-CANNTG-3'). There are different types of E-boxes, depending on the identity of the two central bases. One of the most common is the palindromic G-box (5'-CACGTG-3'). Certain conserved amino acids within the basic region of the protein provide recognition of the core consensus site, whereas other residues in the domain dictate specificity for a given type of E-box . In addition, flanking nucleotides outside of the hexanucleotide core have been shown to play a role in binding specificity, and there is evidence that a loop residue in the protein plays a role in DNA binding through elements that lie outside of the core recognition sequence.

Toledo-Ortiz G, Huq E, Quail PH.
The Arabidopsis basic/helix-loop-helix transcription factor family.
Plant Cell. 2003 Aug;15(8):1749-70
PMID: 12897250