Editing Cell nucleus (section)

===Gene expression===
{{Main|Gene expression}}
{{See also|Transcription factories}}
[[File:Basic diagram of a transcription factory during transcription.png|thumb|upright=1.3|A generic [[Transcription factories|transcription factory]] during transcription, highlighting the possibility of transcribing more than one gene at a time. The diagram includes 8 RNA polymerases however the number can vary depending on cell type. The image also includes transcription factors and a porous, protein core.]]

Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, mRNA produced needs to be exported.<ref>{{cite book |title=Protein Synthesis and Ribosome Structure: Translating the Genome |last1=Nierhaus |first1=Knud H. | first2 = Daniel N. | last2 = Wilson | name-list-style = vanc |year=2004 |publisher=Wiley-VCH |isbn=978-3-527-30638-1 }}</ref>

Since the nucleus is the site of transcription, it also contains a variety of proteins that either directly mediate transcription or are involved in regulating the process. These proteins include [[helicase]]s, which unwind the double-stranded DNA molecule to facilitate access to it, [[RNA polymerase]]s, which bind to the DNA promoter to synthesize the growing RNA molecule, [[topoisomerase]]s, which change the amount of [[supercoil]]ing in DNA, helping it wind and unwind, as well as a large variety of transcription factors that regulate expression.<ref>{{cite book |title=Genome Structure and Function: From Chromosomes Characterization to Genes Technology |last=Nicolini |first=Claudio A. | name-list-style = vanc |year=1997 |publisher=Springer |isbn=978-0-7923-4565-7 }}</ref>