Gene gating
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Gene gating is a phenomenon by which transcriptionally active genes are brought next to nuclear pore complexes (NPCs) so that nascent transcripts can quickly form mature mRNA associated with export factors.[1][2] Gene gating was first hypothesised by Günter Blobel in 1985.[3] It has been shown to occur in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster as well as mammalian model systems.[1]
The proteins that constitute the NPCs, known as nucleoporins, have been shown to play a role in DNA binding and mRNA transport, making gene gating possible. In addition, gene gating is orchestrated by two protein complexes, Spt-Ada-Gcn5-acetyltransferase (SAGA) and transcription–export complex 2 (TREX-2 complex). SAGA is a chromatin remodeling complex responsible for activating the transcription of certain inducible genes. The SAGA complex binds to gene promoters and also interacts with the TREX-2 complex.[4] In turn, the TREX-2 complex interacts with the NPC, thus favouring the relocation of actively transcribed genes to the periphery of the cell nucleus.[2][5] In contrast, the rest of the periphery, i.e. those parts not associated with NPCs, is transcriptionally silent heterochromatin.