BHLH protein

Payne, C.T. et al., GL3 encodes a bHLH protein that regulates trichome development in Arabidopsis through interaction with GLI and TTGl. Genetics, 156, 1349, 2000. 

Zhang F, Gonzalez A, Zhao M, Payne CT, Lloyd A. 2003. A network of redundant bHLH proteins functions in all TTG1-dependent pathways of Arabidopsis. Development 130 4859 4869. 

Myb and bHLH protein-encoding genes have been ectopically expressed in the plant species from which they originated, as well as in heterologous plant species. All studies described here used the cauliflower mosaic virus (CaMV) 35S RNA promoter, which is highly active in most tissues of most plant species, to express the transcription factors. 

Molkentin, J.D., B.L. Black, J.F. Martin, and E.N. Olson (1995). Cooperative activation of muscle gene expression by MEF2 and myogenic bHLH proteins. Cell 83 1125-1136. 

The core of the binding sequence contains the consensus for the binding of bHLH proteins (CANNTG). Any mutation deviating from the UASjno core consensus of 5 CATGTG 3 results in reduced expression (Bachhawat et al., 1995). 

High-resolution structural data are not yet available on the interaction between the HIF heterodimer and the HRE. Interactions between bHLH proteins and DNA have shown that a conserved His-Glu-Arg triad in the bHLH binds in the DNA major groove (11). Modeling studies predict that the HIF-P domain binds to HREs in a similar fashion. HIF-a, however, oifly retains the Arg residue of this conserved triad, and the interaction of HIF with DNA is predicted to be mediated by other residues, specifically a serine and two alanines (12). These proposals are supported by mutagenesis studies (13). 

In strategy II monocots, the key transcriptional regulator of genes involved in phytosiderophore synthesis and iron uptake is the BHLH protein, IR02. A model of the regulatory network has been established. In response... 

A FIGURE 11-22 Interaction of homodimeric leucine-zipper and basic helix-loop-helix (bHLH) proteins with DNA. (a) In... 

Basic Helix-Loop-Helix (bHLH) Proteins The DNA-binding domain of another class of dimeric transcription factors contains a structural motif very similar to the basic-zipper motif except that a nonhelical loop of the polypeptide chain separates two a-helical regions in each monomer (Figure 1 l-22b). Termed a basic helix-loop-helix (bHLH), this motif was predicted from the amino acid sequences of these proteins, which contain an N-terminal a helix with basic residues that interact with DNA, a middle loop region, and a C-termlnal region with hydrophobic amino acids spaced at intervals characteristic of an amphipathic a helix. As with basic-zipper proteins, different bHLH proteins can form heterodimers. 

Four bHLH transcription factors that are remarkably similar to the myogenic bHLH proteins control neurogenesis in Drosophila. Similar proteins appear to function in neurogenesis in vertebrates and perhaps in the determination and differentiation of hematopoietic cells. 

Neurogenesis In Drosophila depends upon a set of four neu rogenic bHLH proteins that are conceptually and stmcturaUy similar to the vertebrate myogenic proteins (see Figure 22-18). 

One of the best examples of dimerization control of transcription-factor function is the interaction of basic helix-loop-helix (bHLH) proteins. Figure 29.5 shows that the interaction between various bHLH proteins can be reflected in the affinity of homo- and heterodimers for specific DNA sequences. Helix-loop-helix proteins lacking the basic region required for DNA binding, can dimerize with bHLH proteins and inhibit their DNA binding activity. These HLH proteins are said to have a dominant negative effect on bHLH proteins because they are dominant repressors of bHLH activity (Fig. 29.5). 

Helix-loop-helix transcription factors are a fourth stractural type of DNA binding protein (see Fig. 16.16D). They also function as dimers that fit around and grip DNA in a manner geometrically similar to leucine zipper proteins. The dimerization region consists of a portion of the DNA-gripping helix and a loop to another helix. Like leucine zippers, helix-loop-helix factors can function as either hetero or homodimers. These factors also contain regions of basic amino acids near the amino terminus and are also called basic helix-loop-helix (bHLH) proteins. 

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