PlantTFDB
Plant Transcription Factor Database
v4.0
Previous version: v1.0, v2.0, v3.0
Artemisia annua
bHLH Family
Species TF ID Description
Aan000961bHLH family protein
Aan003367bHLH family protein
Aan003719bHLH family protein
Aan003774bHLH family protein
Aan003795bHLH family protein
Aan003890bHLH family protein
Aan004069bHLH family protein
Aan004724bHLH family protein
Aan006119bHLH family protein
Aan007250bHLH family protein
Aan007883bHLH family protein
Aan009008bHLH family protein
Aan011806bHLH family protein
Aan012198bHLH family protein
Aan013065bHLH family protein
Aan013081bHLH family protein
Aan013676bHLH family protein
Aan014100bHLH family protein
Aan014185bHLH family protein
Aan014635bHLH family protein
Aan014660bHLH family protein
Aan014676bHLH family protein
Aan014873bHLH family protein
Aan014933bHLH family protein
Aan015017bHLH family protein
Aan015099bHLH family protein
Aan015520bHLH family protein
Aan015856bHLH family protein
Aan016844bHLH family protein
Aan017400bHLH family protein
Aan017432bHLH family protein
Aan018254bHLH family protein
Aan018638bHLH family protein
Aan018887bHLH family protein
Aan018975bHLH family protein
Aan019025bHLH family protein
Aan019228bHLH family protein
Aan019478bHLH family protein
Aan020285bHLH family protein
Aan020328bHLH family protein
Aan020695bHLH family protein
Aan021231bHLH family protein
Aan021257bHLH family protein
Aan021570bHLH family protein
Aan021702bHLH 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