Editing Cell nucleus (section)

===Cell compartmentalization===
The [[nuclear envelope]] allows control of the nuclear contents, and separates them from the rest of the cytoplasm where necessary. This is important for controlling processes on either side of the nuclear membrane: In most cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes in the pathway. This regulatory mechanism occurs in the case of [[glycolysis]], a cellular pathway for breaking down [[glucose]] to produce energy. [[Hexokinase]] is an enzyme responsible for the first step of glycolysis, forming [[glucose-6-phosphate]] from glucose. At high concentrations of [[fructose-6-phosphate]], a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus,<ref name="Lehninger">{{cite book | last1 =Lehninger | first1 =Albert L. | last2 =Nelson | first2 =David L. | last3 =Cox | first3 =Michael M. | name-list-style =vanc | title =Lehninger principles of biochemistry | edition =3rd | year =2000 | publisher =Worth Publishers | location =New York | isbn =978-1-57259-931-4 | url-access =registration | url =https://archive.org/details/lehningerprincip01lehn }}</ref> where it forms a transcriptional repressor complex with nuclear proteins to reduce the expression of genes involved in glycolysis.<ref name="Moreno">{{cite journal | vauthors = Moreno F, Ahuatzi D, Riera A, Palomino CA, Herrero P | title = Glucose sensing through the Hxk2-dependent signalling pathway | journal = Biochemical Society Transactions | volume = 33 | issue = Pt 1 | pages = 265–8 | date = February 2005 | pmid = 15667322 | doi = 10.1042/BST0330265 | s2cid = 20647022 | department = Primary }}</ref>

In order to control which genes are being transcribed, the cell separates some transcription factor proteins responsible for regulating gene expression from physical access to the DNA until they are activated by other signaling pathways. This prevents even low levels of inappropriate gene expression. For example, in the case of [[NF-κB]]-controlled genes, which are involved in most [[inflammation|inflammatory]] responses, transcription is induced in response to a [[cell signaling|signal pathway]] such as that initiated by the signaling molecule [[TNF-α]], binds to a cell membrane receptor, resulting in the recruitment of signalling proteins, and eventually activating the transcription factor NF-κB. A [[nuclear localisation signal]] on the NF-κB protein allows it to be transported through the nuclear pore and into the nucleus, where it stimulates the transcription of the target genes.<ref name="MBoC" />

The compartmentalization allows the cell to prevent translation of unspliced mRNA.<ref name="Gorlich">{{cite journal | vauthors = Görlich D, Kutay U | title = Transport between the cell nucleus and the cytoplasm | journal = Annual Review of Cell and Developmental Biology | volume = 15 | issue = 1 | pages = 607–60 | year = 1999 | pmid = 10611974 | doi = 10.1146/annurev.cellbio.15.1.607 | department = Review }}</ref> Eukaryotic mRNA contains introns that must be removed before being translated to produce functional proteins. The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation. Without the nucleus, ribosomes would translate newly transcribed (unprocessed) mRNA, resulting in malformed and nonfunctional proteins.<ref name = "Lodish" />{{rp|108–15}}