PlantTFDB
Plant Transcription Factor Database
v4.0
Previous version: v1.0, v2.0, v3.0
Selaginella moellendorffii
bHLH Family
Species TF ID Description
114141bHLH family protein
117274bHLH family protein
118904bHLH family protein
128445bHLH family protein
131087bHLH family protein
157919bHLH family protein
16039bHLH family protein
165311bHLH family protein
165556bHLH family protein
24892bHLH family protein
28262bHLH family protein
34848bHLH family protein
39143bHLH family protein
402301bHLH family protein
402536bHLH family protein
402928bHLH family protein
403406bHLH family protein
404767bHLH family protein
405220bHLH family protein
405492bHLH family protein
405883bHLH family protein
407706bHLH family protein
408741bHLH family protein
408928bHLH family protein
409950bHLH family protein
409967bHLH family protein
411158bHLH family protein
411161bHLH family protein
412326bHLH family protein
412681bHLH family protein
413232bHLH family protein
413316bHLH family protein
418491bHLH family protein
419388bHLH family protein
421249bHLH family protein
422169bHLH family protein
424152bHLH family protein
424604bHLH family protein
425336bHLH family protein
430716bHLH family protein
439190bHLH family protein
440893bHLH family protein
443113bHLH family protein
444782bHLH family protein
445783bHLH family protein
56610bHLH family protein
72702bHLH family protein
73360bHLH family protein
75047bHLH family protein
77288bHLH family protein
81013bHLH family protein
91237bHLH family protein
91359bHLH family protein
93546bHLH family protein
94010bHLH 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