PlantTFDB
Plant Transcription Factor Database
v4.0
Previous version: v1.0, v2.0, v3.0
Phalaenopsis equestris
bHLH Family
Species TF ID Description
PEQU_00093bHLH family protein
PEQU_00717bHLH family protein
PEQU_00917bHLH family protein
PEQU_00935bHLH family protein
PEQU_01082bHLH family protein
PEQU_01221bHLH family protein
PEQU_01669bHLH family protein
PEQU_02422bHLH family protein
PEQU_02696bHLH family protein
PEQU_03041bHLH family protein
PEQU_03695bHLH family protein
PEQU_03951bHLH family protein
PEQU_04477bHLH family protein
PEQU_04617bHLH family protein
PEQU_04799bHLH family protein
PEQU_05185bHLH family protein
PEQU_05211bHLH family protein
PEQU_05535bHLH family protein
PEQU_05976bHLH family protein
PEQU_06066bHLH family protein
PEQU_06159bHLH family protein
PEQU_07052bHLH family protein
PEQU_07162bHLH family protein
PEQU_08299bHLH family protein
PEQU_08396bHLH family protein
PEQU_08535bHLH family protein
PEQU_09399bHLH family protein
PEQU_09402bHLH family protein
PEQU_09500bHLH family protein
PEQU_09596bHLH family protein
PEQU_10038bHLH family protein
PEQU_10105bHLH family protein
PEQU_11259bHLH family protein
PEQU_11552bHLH family protein
PEQU_11744bHLH family protein
PEQU_12007bHLH family protein
PEQU_12064bHLH family protein
PEQU_12093bHLH family protein
PEQU_12284bHLH family protein
PEQU_12360bHLH family protein
PEQU_13628bHLH family protein
PEQU_13674bHLH family protein
PEQU_15028bHLH family protein
PEQU_16204bHLH family protein
PEQU_16498bHLH family protein
PEQU_16506bHLH family protein
PEQU_18104bHLH family protein
PEQU_18523bHLH family protein
PEQU_19165bHLH family protein
PEQU_19290bHLH family protein
PEQU_19306bHLH family protein
PEQU_19363bHLH family protein
PEQU_19393bHLH family protein
PEQU_19717bHLH family protein
PEQU_19869bHLH family protein
PEQU_20513bHLH family protein
PEQU_21534bHLH family protein
PEQU_21779bHLH family protein
PEQU_21851bHLH family protein
PEQU_22352bHLH family protein
PEQU_23361bHLH family protein
PEQU_24260bHLH family protein
PEQU_24299bHLH family protein
PEQU_24356bHLH family protein
PEQU_24669bHLH family protein
PEQU_24707bHLH family protein
PEQU_25174bHLH family protein
PEQU_25584bHLH family protein
PEQU_26133bHLH family protein
PEQU_26619bHLH family protein
PEQU_26890bHLH family protein
PEQU_28467bHLH family protein
PEQU_28725bHLH family protein
PEQU_30280bHLH family protein
PEQU_30340bHLH family protein
PEQU_30391bHLH family protein
PEQU_30601bHLH family protein
PEQU_30652bHLH family protein
PEQU_31322bHLH family protein
PEQU_31370bHLH family protein
PEQU_31776bHLH family protein
PEQU_33149bHLH family protein
PEQU_33912bHLH family protein
PEQU_34950bHLH family protein
PEQU_36063bHLH family protein
PEQU_36710bHLH family protein
PEQU_37291bHLH family protein
PEQU_37567bHLH family protein
PEQU_38095bHLH family protein
PEQU_38610bHLH family protein
PEQU_39608bHLH family protein
PEQU_39939bHLH family protein
PEQU_40864bHLH family protein
PEQU_41106bHLH family protein
PEQU_41947bHLH family protein
PEQU_42108bHLH 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