Considering that gene expression results in the formation of a polypeptide, it can be regulated at several levels. In eukaryotes, the regulation could be exerted at
(i) transcriptional level (formation of primary transcript)
(ii) processing level (regulation of splicing)
(iii) transport of mRNA from nucleus to the cytoplasm
(iv) translational level

While, in prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression.

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