Plant Transcription Factor Database
Previous version: v3.0
Saccharum officinarum
bHLH Family
Species TF ID Description
Sof000566bHLH family protein
Sof000735bHLH family protein
Sof000809bHLH family protein
Sof001089bHLH family protein
Sof001415bHLH family protein
Sof001677bHLH family protein
Sof001891bHLH family protein
Sof002214bHLH family protein
Sof002972bHLH family protein
Sof003412bHLH family protein
Sof003420bHLH family protein
Sof003501bHLH family protein
Sof003940bHLH family protein
Sof004211bHLH family protein
Sof005144bHLH family protein
Sof005297bHLH family protein
Sof005318bHLH family protein
Sof005889bHLH family protein
Sof007067bHLH family protein
Sof007200bHLH family protein
Sof007425bHLH family protein
Sof008554bHLH family protein
Sof009294bHLH family protein
Sof009808bHLH family protein
Sof010049bHLH family protein
Sof010409bHLH family protein
Sof011450bHLH family protein
Sof011483bHLH family protein
Sof011588bHLH family protein
Sof011892bHLH family protein
Sof012104bHLH family protein
Sof012700bHLH family protein
Sof013715bHLH family protein
Sof014383bHLH family protein
Sof014972bHLH family protein
Sof015154bHLH family protein
Sof015514bHLH family protein
Sof015767bHLH family protein
Sof016489bHLH family protein
Sof017300bHLH family protein
Sof017491bHLH family protein
Sof017546bHLH family protein
Sof017779bHLH family protein
Sof020010bHLH family protein
Sof020050bHLH family protein
Sof020809bHLH family protein
Sof020909bHLH family protein
Sof021181bHLH 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