Mediator forms a large protein complex that binds to the C-terminal domain of the RNA polymerase II holoenzyme, acting as a bridge between this enzyme and transcription factors.
Mediator, first identified in Saccharomyces cerevisiae, is the central coactivator of transcription in eukaryotes ranging from yeast to humans. Therefore, it is important to evaluate the phenotype and target gene expression in a VP16 fusion line and multiple-knockout lines, and show how functional conversion by VP16 fusion occurs in plants. Furthermore, the molecular mechanism of VP16 transcriptional activation in plants is unknown.
This result suggests that there are cases in which VP16 fusion to the transcriptional repressor fails to convert the function. reported that VP16 transactivation activity is strongly inhibited by fusion with the tobacco ETHYLENE RESPONSIVE ELEMENT BINDING FACTOR 3 (ERF3) fragment containing a repression motif. However, data is lacking which compares the phenotype and target gene expression in multiple-knockout lines and the VP16-fusion line to show how much the VP16 fusion system is capable of inducing a strong phenotype, which can only be seen in multiple-knockout lines, such as in the CRES-T system. Several reports have shown that fusion with VP16 is capable of turning a repressive transcription regulator into an activator, which causes a similar or stronger phenotype compared to those of knockout Arabidopsis plants. A promising technique besides CRES-T is conversion of transcriptional repressors to activators by fusion with the strong transactivation domain of VP16 (hereafter called “VP16”), which has been isolated from the herpes simplex virus. However, this technique is ineffective for native transcriptional repressors to cause thier knockout phenotypes, and progress in transcriptional repressor functional analyses has been hampered by gene redundancy.
CRES-T causes a strong, dominant phenotype, which can often be observed only by multiple-knockout mutations of redundant genes.
#Srdx as a suppressor for transcription factors Activator#
CRES-T is a powerful plant gene silencing system, which converts a transcriptional activator into a strong repressor by fusion with a plant-specific small repression peptide SRDX, which contains the plant-specific repression motif xLxLxL named EAR motif. CRES-T (Chimeric REpressor gene Silencing Technology) is one technique that solves such problems and is now widely used in basic and applied research. Most single loss-of-function mutants in Arabidopsis do not show any detectable phenotype because of gene redundancy, which makes gene function analysis difficult.
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