Nin-like Transcription Factor Family
Nodule inception initially relies on cell competence in a narrow infection zone located
just behind the growing root tip. Older nodules then regulate the number of nodules on
a root system by suppressing the development of nodule primordia.Nin (for nodule
inception) is required for the formation of infection threads and the initiation of
primordia. NIN protein has regional similarity to transcription factors, and the
predicted DNA-binding/dimerization domain identifies and typifies a consensus motif
conserved in plant proteins with a function in nitrogen-controlled development.
The full-length Nin cDNA has an open reading frame of 2,634 bp, a 5' leader with stop
codons in all three reading frames, and a 3' untranslated region of 141 bp. The
protein, comprising 878 amino acids, is shown in Fig. 3a along with a diagram of
several domains with similarity to transcription factors. The carboxy-terminal half of
the protein carries an unusual putative DNA-binding domain with a basic region followed
by two heptad leucine or isoleucine repeats (R1 and R2); an amphiphatic leucine-zipper
structure was predicted for R2 by helical-wheel analysis (Fig. 3). This arrangement is
similar to the DNA-binding/dimerization domains of the bZIP8 and bHLH/Z9 transcription
factors, but the R1/R2 region does not comply with a strict consensus of either domain.
The distance between the basic region and the zipper, for example, is longer than would
be expected from the bZIP consensus. The presence of a proline helix breaker (Pro 597)
in R1 also distinguishes NIN, and alignment to prokaryotic helix?Cturn?Chelix
DNA-binding domains10 suggests a GV turn motif preceding Pro 597 (not shown). No known
DNA-binding/dimerization domains combine these components, and the structure of the
domain has yet to be resolved by crystallography. Two acidic domains located between
residues 428?C503 and 826?C845 may function as transcriptional activation domains.
Supporting the role as a transcription factor, NIN has SV40-like and bipartite nuclear
localization signals11 (Fig. 3). Less clear is the role of a hexaglutamine stretch
between residues 9?C14 and five double and eight single glutamine residues within the
first 420 amino acids.
The nitrogen regulation of nodule organogenesis and Chlamydomonas gametogenesis
together with the conserved domain embedding the RWP?CRK motif of NIN and Mid indicate
that this domain is involved in the regulation of genes controlled by nitrogen status.
Because the conserved domain was found only in proteins from algae and higher plants,
this class of regulator proteins probably evolved after the common ancestor of algae
and plants diverged from the other eukaryotes.
(taken from
PlantTFDB
and TOBFAC).
Notes: Nin-like family is missed in PlnTFDB.
14 Nin-like predicted putative sequences,
blast HSP, and multiple sequence alignment in
Soy - TFKB.
3 Nin-like protein and DNA sequences with
annotations for soybean in PlantTFDB.
Last updated by Dr. Jeff Chen on July 20, 2009.