Gene gating hypothesis

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. Gene gating was first hypothesised by Günter Blobel in 1985. It has been shown to occur in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster as well as mammalian model systems.

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. 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. In contrast, the rest of the periphery, i.e. those parts not associated with NPCs, is transcriptionally silent heterochromatin.

Nucleoporins (Nups) are the main constituent proteins of NPCs and have been shown to play multiple roles in mediating several processes involved in gene gating. While it has been known that the nuclear periphery serves as the primary location for most heterochromatin, telomeric and centrosomal DNA, studies in the yeast Saccharomyces cerevisiae have shown that NPCs containing Nup2p and Prp20p create boundaries of active gene expression near the nuclear envelope and prevent the spread of heterochromatin at the nuclear periphery. These Nup2p and Prp20p proteins also provide a location for the binding of chromatin.

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