NAC transcription factor: Difference between revisions

Vascular-related NAC-domain transcription facor (VND) is one group of the largest plant-specific transcription factor NAC family. The VND1-VND7 were orginally isolated as genes for which expression levels are elevated during transdifferentiation into trachery elements, in a induction system using Arabidopsis suspension cells <ref name="GENEDEV">http://genesdev.cshlp.org/content/19/16/1855.full.pdf</ref>.In the past several years, VNDs have been intensively investigated in different species and shown to be important switches of the biosynthesis of secondary cell walls that provide textiles, timber, and potentially second-generation bio-fuels for human use<ref>http://mplant.oxfordjournals.org/content/early/2011/12/01/mp.ssr098.full.pdf+html

</ref><ref name="MPLANT">http://www.springerlink.com/content/qq1584g690243n16/fulltext.pdf

</ref>. Typically, the proteins in this subfamily share a well conserved N-terminal NAC domain (-150 amino acid;aa) and a diversified C-terminal transcription regulatory region  <ref>www.ncbi.nlm.nih.gov/pubmed/15708345</ref> <ref name ="nature">http://www.nature.com/embor/journal/v5/n3/pdf/7400093.pdf</ref>. The N-terminal NAC domain is usually responsible for DNA binding and dimerization, and the C-terminal region function in transcription activation , repression and protein binding. X-ray crystallography have exhibited the structure of conserved NAC domains when they form dimer and bind with DNA. However, due to the diversified sequence of C-terminal region, no structure analyses haven't been conducted in the region.

The DNA binding activity of NAC proteins is restricted into NAC domain which was divided into five subdomains A-E. The highly conserved positively charged subdomains C and D bind to DNA, whereas subdomain A may be involved in the formation of a functional dimer. X-ray crystallograhy  have exhibited the presence of a novel transcription factor fold consisting of a twirled antiparallel β-sheet (β 1-6/7) which is used for DNA binding,located between an N-terminal helix and a short helix  <ref name="ncbi">www.ncbi.nlm.nih.gov/pubmed/21337010</ref> <ref>http://www.springerlink.com/content/8p88600115713107/fulltext.pdf</ref>. Most importantly, Val119-Ser183, lys123 and lys126, along with Lys79, Arg85,and Arg 88 were identified as biochemically crucial for DNA binding. Arg88 is conserved in all NAC proteins but Lys79 and Arg85 could be exchangable but exert different DNA binding affinity  <ref>http://www.springerlink.com/content/r27215773758j405/fulltext.pdf</ref>. The NAC domain-fold also modulates dimerization through Leu14–Thr23 and Glu26–Tyr31 residues, which form a short antiparallel b-sheet at the dimer

interface stabilized by salt bridges formed by Arg19 and Glu26  <ref name ="nature">http://www.nature.com/embor/journal/v5/n3/pdf/7400093.pdf</ref> <ref name="ncbi">www.ncbi.nlm.nih.gov/pubmed/21337010</ref> . This domain also contains mono or bipartite nuclear localization signals with the lysine residues in subdomain D playing crucial roles for nuclear shuttling  <ref name="MPLANT">http://www.springerlink.com/content/qq1584g690243n16/fulltext.pdf