ARCHITECTURE CHARACTERISTICS OF BZIP TRANSCRIPTION FACTORS
Transcription factor (TF), also
known as trans -acting factor, is a category of proteins that can
specifically bind to cis -acting elements in the promoter region
of eukaryotic genes, thereby activating or silencing the expression of
related genes in a specific time and space. The structure of plant
transcription factors generally includes at least four functional
domains, including the DNA binding domain, the transcriptional
regulatory domain, the nuclear localization signal and the
oligomerization site (Du et al., 2012). They work together to regulate
various biological processes.
Although the classification of
bZIP varies depending on the researcher’s choice, there is currently a
consensus on this type of transcription factor that the protein sequence
contains a conserved bZIP domain with 60-80 amino acids length. This
domain is consisted of at least two specific structures. Firstly, the
N-terminus is a basic region composed of about 20 basic amino acids,
containing a nuclear localization signal (NLS) and a N-x7-R/K structural
unit that specifically binds to a DNA sequence. This region is involved
in nuclear localization and DNA binding (Lee et al., 2006b). Secondly,
the C-terminus, which is a leucine zipper region, a heptad repeat of
leucine or other bulky hydrophobic amino acids (Ile, Val, Phe, or Met)
positioned exactly nine amino acids towards the C-terminus, creating an
amphipathic helix. This region is involved in the dimerization of the
bZIP protein before it binds to DNA (Hurst, 1994; Jakoby et al., 2002;
Landschulz et al., 1988). In addition to the bZIP conserved domain, the
bZIPs also contain other domains with transcriptional activation
functions, such as the R/KxxS/T and S/TxxD domains, which are
phosphorylation sites of Ca2+ independent protein
kinase and casein kinase II (Furihata et al., 2006). Besides, there are
also some regions rich in acidic amino acids such as Pro and Gln, which
can activate the transcriptional expression of downstream target genes
(Liao et al., 2008).