Srdx recognition domain3/15/2023 ![]() Following its discovery in CBP, KIX domain has been identified in the human activator recruited cofactor 105-kDa component (ARC105) and yeast Gal11p both of which are mediator of RNA polymerase II (RNA Pol II) transcription subunit 15 (MED15) subunit of mediator complex involved in regulation of transcription of specific genes ( 2–4). Since its initial identification was based on its interaction with the phosphorylated kinase-inducible domain (KID) region of CREB protein, it was given the name ‘KID-interacting domain’ or ‘KIX’ ( 1). ( 1), in 1996 in the mouse CBP, as the specific and minimal region that was sufficient to bind and interact with phosphorylated CREB and then activate transcription. One of the domains of CBP is a vital, independently folding and highly conserved three-helix bundle region termed as the kinase-inducible domain interacting (KIX) domain. One such coactivator is the cAMP-response element-binding protein (CREB)-binding protein (CBP), a large multi-domain protein containing stretches of intrinsically disordered linker regions and a number of structured protein-binding domains that interact with a large variety of transcription factors. These coactivators thus serve as bridging molecules between transcription factors and the transcription machinery, or as enzymes that introduce chemical modifications on DNA. In addition, transcription factors mediate recruitment of other factors, subsequent chromatin modification and pre-initiation complex formation by docking one or more of their transactivation domains to conserved sites on many cognate proteins, like, for example, transcriptional coactivators that are important binding partners for activation domains (ADs). Transcriptional activators achieve gene specificity by binding specific regulatory elements on DNA via functionally independent DNA-binding domains. Its regulation in eukaryotes is accomplished through an intricate network of specific interactions at the DNA–protein interface and the protein–protein interface. Transcriptional activation is a key process in the regulation of gene expression in living organisms, and more so in eukaryotes where the transcriptional apparatus is a huge modular complex. We also discuss the possible roles of KIX domains in plants and hope that this review will accelerate scientific interest in KIX and pave the way for novel avenues of research on this critical domain. In this article, we review the KIX domain in terms of its sequence and structure and present the various implications of its ability to act as a transcriptional switch, the mechanistic basis of molecular recognition by KIX, its binding specificity, target promiscuity, combinatorial potential and unique mode of regulation via allostery. Their targets are often intrinsically disordered regions within the transactivation domains of transcription factors that attain stable secondary structure only upon complexation with KIX. KIX domains have been characterized in transcriptional coactivators such as p300/CREB-binding protein and mediator of RNA polymerase II transcription subunit 15, and even recQ protein-like 5 helicases in various organisms. This docking event is a harbinger of an intricate multi-protein assembly at the transcriptional apparatus and is regulated in a highly precise manner in view of the critical role it plays in multiple cellular processes. Transient effector-reporter assays for functional analysis of transcription factors and detection of protein-protein interactions using the trans-repressive activity of SRDX repression domain are also described.The kinase-inducible domain interacting (KIX) domain is a highly conserved independently folding three-helix bundle that serves as a docking site for transcription factors, whereupon promoter activation and target specificity are achieved during gene regulation. Strategies for construction of the chimeric repressors and their expression in transgenic plants are described. This system is simple and effective and can be used as a powerful tool not only for functional analysis of redundant transcription factors but also for the manipulation of plant traits by active suppression of the gene expression. As a result, the transgenic plants that express a chimeric repressor exhibit phenotypes similar to loss-of-function of the alleles of the gene encoding the transcription factor. In this system, a chimeric repressor that is produced by fusion of a transcription factor to the plant-specific EAR-motif repression domain (SRDX) suppresses target genes of a transcription factor dominantly over the activity of endogenous and functionally redundant transcription factors. ![]() Chimeric REpressor gene Silencing Technology (CRES-T) is a useful tool for functional analysis of plant transcription factors. ![]()
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