<P> Any step of gene expression may be modulated, from the DNA - RNA transcription step to post-translational modification of a protein . The following is a list of stages where gene expression is regulated, the most extensively utilised point is Transcription Initiation: </P> <Ul> <Li> Chromatin domains </Li> <Li> Transcription </Li> <Li> Post-transcriptional modification </Li> <Li> RNA transport </Li> <Li> Translation </Li> <Li> mRNA degradation </Li> </Ul> <P> In eukaryotes, the accessibility of large regions of DNA can depend on its chromatin structure, which can be altered as a result of histone modifications directed by DNA methylation, ncRNA, or DNA - binding protein . Hence these modifications may up or down regulate the expression of a gene . Some of these modifications that regulate gene expression are inheritable and are referred to as epigenetic regulation . </P> <P> Transcription of DNA is dictated by its structure . In general, the density of its packing is indicative of the frequency of transcription . Octameric protein complexes called nucleosomes are responsible for the amount of supercoiling of DNA, and these complexes can be temporarily modified by processes such as phosphorylation or more permanently modified by processes such as methylation . Such modifications are considered to be responsible for more or less permanent changes in gene expression levels . </P>

When is gene expression regulated in eukaryotic cells
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