Levels of control of eukaryotic gene expression

In principle, expression can be regulated at four
distinct levels. The first and by far the most important
is primary control of transcription.
Processing to mature RNA can be regulated at
the level of the primary RNA transcript. A
frequently observed process is alternative splicing
(see D). Translation can be varied by RNA
editing (see B for an example). At the protein
level, posttranslational modifications can determine
the activity of a protein. The cleavage of
preproinsulin to form mature insulin, glycosylation
or hydroxylation, and protein folding