PlantTFDB
Plant Transcription Factor Database
v4.0
Previous version: v1.0, v2.0, v3.0
Citrullus lanatus
bHLH Family
Species TF ID Description
Cla000121bHLH family protein
Cla000218bHLH family protein
Cla000703bHLH family protein
Cla001226bHLH family protein
Cla001331bHLH family protein
Cla001652bHLH family protein
Cla001653bHLH family protein
Cla001654bHLH family protein
Cla001663bHLH family protein
Cla001713bHLH family protein
Cla002643bHLH family protein
Cla002645bHLH family protein
Cla002749bHLH family protein
Cla003232bHLH family protein
Cla003821bHLH family protein
Cla003872bHLH family protein
Cla004098bHLH family protein
Cla004232bHLH family protein
Cla005253bHLH family protein
Cla005872bHLH family protein
Cla006006bHLH family protein
Cla006058bHLH family protein
Cla006061bHLH family protein
Cla006230bHLH family protein
Cla006231bHLH family protein
Cla006289bHLH family protein
Cla006599bHLH family protein
Cla006673bHLH family protein
Cla006692bHLH family protein
Cla006693bHLH family protein
Cla007559bHLH family protein
Cla007697bHLH family protein
Cla007867bHLH family protein
Cla007965bHLH family protein
Cla008442bHLH family protein
Cla008700bHLH family protein
Cla008805bHLH family protein
Cla008880bHLH family protein
Cla008890bHLH family protein
Cla009965bHLH family protein
Cla010083bHLH family protein
Cla010220bHLH family protein
Cla010338bHLH family protein
Cla010508bHLH family protein
Cla010576bHLH family protein
Cla010807bHLH family protein
Cla010890bHLH family protein
Cla011198bHLH family protein
Cla011292bHLH family protein
Cla011510bHLH family protein
Cla012633bHLH family protein
Cla012667bHLH family protein
Cla013237bHLH family protein
Cla013532bHLH family protein
Cla013555bHLH family protein
Cla013612bHLH family protein
Cla014072bHLH family protein
Cla014073bHLH family protein
Cla014074bHLH family protein
Cla014085bHLH family protein
Cla014109bHLH family protein
Cla014246bHLH family protein
Cla014286bHLH family protein
Cla014806bHLH family protein
Cla014822bHLH family protein
Cla014905bHLH family protein
Cla014991bHLH family protein
Cla015223bHLH family protein
Cla015458bHLH family protein
Cla015607bHLH family protein
Cla015818bHLH family protein
Cla015913bHLH family protein
Cla016013bHLH family protein
Cla016070bHLH family protein
Cla016091bHLH family protein
Cla016199bHLH family protein
Cla016224bHLH family protein
Cla016562bHLH family protein
Cla016834bHLH family protein
Cla016925bHLH family protein
Cla017143bHLH family protein
Cla017516bHLH family protein
Cla017518bHLH family protein
Cla017925bHLH family protein
Cla018085bHLH family protein
Cla018502bHLH family protein
Cla018537bHLH family protein
Cla018581bHLH family protein
Cla018626bHLH family protein
Cla018722bHLH family protein
Cla018860bHLH family protein
Cla018968bHLH family protein
Cla019030bHLH family protein
Cla019121bHLH family protein
Cla019311bHLH family protein
Cla019510bHLH family protein
Cla019678bHLH family protein
Cla019752bHLH family protein
Cla019764bHLH family protein
Cla019871bHLH family protein
Cla019998bHLH family protein
Cla020193bHLH family protein
Cla020330bHLH family protein
Cla020364bHLH family protein
Cla020607bHLH family protein
Cla020660bHLH family protein
Cla020789bHLH family protein
Cla021059bHLH family protein
Cla021148bHLH family protein
Cla021422bHLH family protein
Cla021661bHLH family protein
Cla021708bHLH family protein
Cla021863bHLH family protein
Cla021887bHLH family protein
Cla021901bHLH family protein
Cla022045bHLH family protein
Cla022119bHLH family protein
Cla022160bHLH family protein
Cla022177bHLH family protein
Cla022582bHLH family protein
Cla022588bHLH family protein
Cla022622bHLH family protein
Cla022649bHLH family protein
Cla022767bHLH family protein
Cla023083bHLH family protein
Cla023247bHLH 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