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Wrky transcription factor

The meaning of «wrky transcription factor»

WRKY transcription factors (pronounced ‘worky’) are proteins that bind DNA. They are transcription factors that regulate many processes in plants and algae (Viridiplantae), such as the responses to biotic and abiotic stresses, senescence, seed dormancy and seed germination and some developmental processes[1][2] but also contribute to secondary metabolism.[3]

Like many transcription factors, WRKY transcription factors are defined by the presence of a DNA-binding domain; in this case, it is the WRKY domain. The WRKY domain was named in 1996 after the almost invariant WRKY amino acid sequence at the N-terminus and is about 60 residues in length. In addition to containing the ‘WRKY signature’, WRKY domains also possess an atypical zinc-finger structure at the C-terminus (either Cx4-5Cx22-23HxH or Cx7Cx23HxC). Most WRKY transcription factors bind to the W-box promoter element that has a consensus sequence of TTGACC/T.

Individual WRKY proteins do appear in the human protozoan parasite Giardia lamblia and slime mold Dictyostelium discoideum.[4]

WRKY transcription factors are denoted by a 60-70 amino acid WRKY protein domain composed of a conserved WRKYGQK motif and a zinc-finger region.[5] Based on the amino acid sequence WRKY transcription factors are classified into three major categories, group I, group II, and group III. Group I WRKY proteins are primarily denoted by the presence of two WRKY protein domains, whereas both groups II and III each possess only one domain. Group III WRKY proteins have a C2HC zinc finger instead of the C2H2 motif of group I and II factors. The structure of several plant WRKY domains has been elucidated using crystallography[6] and nuclear magnetic resonance spectroscopy.[7]

As soon as the WRKY domain was characterized, it was suggested that it contained a novel zinc finger structure and the first evidence to support this came from studies with 2-phenanthroline that chelates zinc ions. Addition of 2-phenenthroline to gel retardation assays that contained E. coli expressed WRKY proteins resulted in a loss of binding to the W-box target sequence. The other suggestion was that the WRKY signature amino acid sequence at the N-terminus of the WRKY domain directly binds to the W-box sequence in the DNA of target promoters. These suggestions were shown to be correct by publication of the solution structure of the C-terminal WRKY domain of the Arabidopsis WRKY4 protein. The WRKY domain was found to form a four-stranded β-sheet.[8] Soon afterwards, a crystal structure of the C-terminal WRKY domain of the Arabidopsis WRKY1 protein was reported. This showed a similar result to the solution structure except that it may contain an additional β-strand at the N-terminus of the domain.[9] From these two studies it appears that the conserved WRKYGQK signature amino acid sequence enters the major groove of the DNA to bind to the W-Box. Recently, the first structural determination of the WRKY domain complexed with a W-Box was reported. The NMR solution structure of the WRKY DNA-binding domain of Arabidopsis WRKY4 in complex with W Box DNA revealed that part of a four-stranded β-sheet enters the major groove of DNA in an atypical mode that the authors named the β-wedge, where this sheet is almost perpendicular to the DNA helical axis. As initially predicted, amino acids in the conserved WRKYGQK signature motif contact the W Box DNA bases mainly through extensive apolar contacts with thymine methyl groups. These structural data explain the conservation of both the WRKY signature sequence at the N-terminus of the WRKY domain and the conserved cysteine and histidine residues. It also provides the molecular basis for the previously noted remarkable conservation of both the WRKY amino acid signature sequence and the W Box DNA sequence.[10]

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