Plant Transcription Factor Database
Previous version: v3.0
Picea glauca
bHLH Family
Species TF ID Description
Pgl000613bHLH family protein
Pgl001021bHLH family protein
Pgl003317bHLH family protein
Pgl003614bHLH family protein
Pgl004180bHLH family protein
Pgl004210bHLH family protein
Pgl004783bHLH family protein
Pgl005354bHLH family protein
Pgl005883bHLH family protein
Pgl006119bHLH family protein
Pgl006469bHLH family protein
Pgl006686bHLH family protein
Pgl007029bHLH family protein
Pgl007083bHLH family protein
Pgl007127bHLH family protein
Pgl008817bHLH family protein
Pgl008851bHLH family protein
Pgl008945bHLH family protein
Pgl009190bHLH family protein
Pgl009212bHLH family protein
Pgl009336bHLH family protein
Pgl009413bHLH family protein
Pgl009765bHLH family protein
Pgl009779bHLH family protein
Pgl009873bHLH family protein
Pgl009970bHLH family protein
Pgl010118bHLH family protein
Pgl010253bHLH family protein
Pgl011006bHLH family protein
Pgl012408bHLH family protein
Pgl012741bHLH family protein
Pgl013029bHLH family protein
Pgl014783bHLH family protein
Pgl015453bHLH family protein
Pgl015556bHLH family protein
Pgl015706bHLH family protein
Pgl015755bHLH family protein
Pgl016091bHLH family protein
Pgl016155bHLH family protein
Pgl017540bHLH family protein
Pgl017702bHLH family protein
Pgl017872bHLH 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