What is an operon in a eukaryotic cell, and how does it regulate the expression of genes? I've already read Wikipedia, but it is not enough clear to me. Unfortunately my knowledge in genetics are very poor!

  • $\begingroup$ You could check out the Encyclopedia Britannica. $\endgroup$
    – HDE 226868
    Dec 29, 2014 at 13:55
  • $\begingroup$ There are some naturally occurring polycistronic mRNAs in flies and worms. You can also make artificial polycistronic DNA using IRES sites or self-cleaving 2A peptide sequences (which were isolated from viruses). Which one are you asking? $\endgroup$
    – Superbest
    Dec 29, 2014 at 16:31
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    $\begingroup$ Is an operon just several genes with the same regulation, so they are transcribed at the same time? In prokaryotes the genes in an operon are often placed next to each other so they can be transcribed as one mRNA and take advantage of their ability to translate polycistronic mRNA, but in eukaryotes where polycistronic mRNAs are less common, they might not need to be near each other in the genome. $\endgroup$
    – user137
    Dec 29, 2014 at 17:19
  • $\begingroup$ @Superbest: I'm asking about naturally occurring polycistronic mRNAs $\endgroup$
    – Salvator
    Dec 30, 2014 at 9:06

1 Answer 1


Operons were once thought to appear only in prokaryotes (and viruses of prokaryotes), but there are now known to be a number examples in eukaryotic organisms. These are mostly seen in nematodes and insects.

Generally an operon is a functional DNA unit which contains a cluster of genes which are regulated by one promoter/repressor element and which are transcribed together. These are genes which functionally work together in a close context. A good example for this is the lac operon in bacteria.

In prokaryotes the expression of the operon leads to polycistronic (multiple open reading frames on the same transcript) mRNA, which is then translated into proteins.

Operons in eukaryotes are also gene clusters (often of functional closely related proteins), which are regulated by one regulatory unit (promoter). See figure 1 from reference 1:

enter image description here

There are different ways of mRNA arising from this phenomenon. First the mRNA can be dicistronic and most likely has internal ribosome entry sites (IRES) which allows the initiation (or re-initiation) of the translation of the second gene. Another possibility is the cleavage of the primary mRNA strand into two (or more) monocistronic mRNAs. And finally it is also possible that the dicistronic transcript is alternatively spliced to get different (monocistronic) mRNAs.

If you are interested in the details of eukaryotic operons, I strongly recommend reading at least the first reference (and probably also following up some of the related citations (on the right on the NIH website)).


  1. Blumenthal, T. (2004). Operons in eukaryotes. Briefings in Functional Genomics, 3(3), 199-211.
  2. Pi, H., Lee, L. W., & Lo, S. J. (2009). New insights into polycistronic transcripts in eukaryotes. Chang Gung Med. J, 32, 494-498.
  • $\begingroup$ One of the best examples for eukaryotic operonic RNAs can be miRNAs produced from clusters. They arise from same primary transcript. $\endgroup$
    Dec 30, 2014 at 6:46
  • $\begingroup$ Since the OP specifically asks about eukaryotic operons, and appears to be understand prokaryotic ones, is it possible to at least also include a diagram of a eukaryotic one? The fly Adh/Adhr paper has a simple figure, but I haven't had time to read it very thoroughly. $\endgroup$
    – Superbest
    Dec 30, 2014 at 16:28
  • $\begingroup$ +1 for using c elegans and drosophila examples in your answer $\endgroup$
    – rhill45
    Jan 1, 2015 at 1:35

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