PlantTFDB
Plant Transcription Factor Database
v4.0
Previous version: v1.0, v2.0, v3.0
Spirodela polyrhiza
bHLH Family
Species TF ID Description
Spipo0G0055600bHLH family protein
Spipo0G0106900bHLH family protein
Spipo0G0119700bHLH family protein
Spipo0G0119800bHLH family protein
Spipo0G0129300bHLH family protein
Spipo0G0136300bHLH family protein
Spipo0G0138300bHLH family protein
Spipo0G0141700bHLH family protein
Spipo0G0154500bHLH family protein
Spipo0G0177000bHLH family protein
Spipo0G0178700bHLH family protein
Spipo10G0014800bHLH family protein
Spipo10G0022600bHLH family protein
Spipo10G0023000bHLH family protein
Spipo10G0038200bHLH family protein
Spipo10G0049800bHLH family protein
Spipo11G0036800bHLH family protein
Spipo12G0015100bHLH family protein
Spipo12G0035300bHLH family protein
Spipo13G0027100bHLH family protein
Spipo13G0027200bHLH family protein
Spipo13G0048400bHLH family protein
Spipo14G0011300bHLH family protein
Spipo14G0021700bHLH family protein
Spipo14G0053900bHLH family protein
Spipo14G0054200bHLH family protein
Spipo15G0002000bHLH family protein
Spipo15G0021500bHLH family protein
Spipo15G0027500bHLH family protein
Spipo16G0020500bHLH family protein
Spipo17G0000700bHLH family protein
Spipo17G0012400bHLH family protein
Spipo17G0016400bHLH family protein
Spipo17G0023400bHLH family protein
Spipo18G0016100bHLH family protein
Spipo18G0027600bHLH family protein
Spipo18G0034900bHLH family protein
Spipo19G0011600bHLH family protein
Spipo19G0034700bHLH family protein
Spipo1G0014100bHLH family protein
Spipo1G0030900bHLH family protein
Spipo1G0068700bHLH family protein
Spipo1G0068800bHLH family protein
Spipo1G0077400bHLH family protein
Spipo1G0124800bHLH family protein
Spipo21G0025300bHLH family protein
Spipo21G0028000bHLH family protein
Spipo22G0007100bHLH family protein
Spipo22G0031100bHLH family protein
Spipo22G0040700bHLH family protein
Spipo25G0005800bHLH family protein
Spipo25G0017500bHLH family protein
Spipo25G0018200bHLH family protein
Spipo26G0002300bHLH family protein
Spipo26G0027000bHLH family protein
Spipo27G0007100bHLH family protein
Spipo28G0003900bHLH family protein
Spipo28G0004200bHLH family protein
Spipo28G0022400bHLH family protein
Spipo2G0038500bHLH family protein
Spipo2G0056200bHLH family protein
Spipo2G0058000bHLH family protein
Spipo2G0107000bHLH family protein
Spipo2G0126200bHLH family protein
Spipo32G0006400bHLH family protein
Spipo3G0050600bHLH family protein
Spipo3G0093200bHLH family protein
Spipo3G0094800bHLH family protein
Spipo4G0017100bHLH family protein
Spipo4G0018600bHLH family protein
Spipo4G0044300bHLH family protein
Spipo4G0062100bHLH family protein
Spipo4G0067600bHLH family protein
Spipo4G0089600bHLH family protein
Spipo4G0090900bHLH family protein
Spipo4G0113200bHLH family protein
Spipo5G0011800bHLH family protein
Spipo5G0021700bHLH family protein
Spipo5G0040800bHLH family protein
Spipo6G0020000bHLH family protein
Spipo6G0025700bHLH family protein
Spipo6G0039300bHLH family protein
Spipo6G0041100bHLH family protein
Spipo6G0041200bHLH family protein
Spipo6G0041300bHLH family protein
Spipo6G0041600bHLH family protein
Spipo6G0041700bHLH family protein
Spipo6G0052700bHLH family protein
Spipo7G0006000bHLH family protein
Spipo7G0049300bHLH family protein
Spipo8G0021500bHLH family protein
Spipo8G0037900bHLH family protein
Spipo8G0047400bHLH family protein
Spipo8G0051500bHLH 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