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What is the purpose of these parts in the translation process ? Picture to demonstrate below :

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The regions between the genes on a prokaryote operon are transcribed into the messenger RNA but are not translated into proteins. Because they are not translated, they are characterized by the general term UnTranslated Regions (UTRs). A typical operon having two genes is shown in this diagram from Wikipedia:

enter image description here

The UTR which occurs between the protein-coding genes contains the sequence for a ribosomal binding site (RBS) in the transcribed mRNA. An RBS is a site where a ribosome can attach to the mRNA so that the Start codon of the following gene is in the correct position to begin translation of the protein. (Of course, the 5' UTR preceding the first gene also has an RBS sequence.) An RBS contains a particular nucleotide sequence to match up with a complementary sequence of the ribosomal RNA of the ribosome; this sequence is known as the Shine-Dalgarno sequence.

(Note that these inter-gene UTRs are not called introns; introns occur only in eukaryotes and occur within a gene, between the Start and Stop codons.)

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  • $\begingroup$ You might add, in answer to the specific question of "purpose", that having separate RBSs allows the independent translation of the cistrons in a polycistronic mRNA, i.e. each cistron can be translated at a different rate producing different amounts of protein product. $\endgroup$ – David Oct 3 '18 at 21:07
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Not sure about the role in this particular case of lac operon but normally such noncoding sequences in eukaryotic system (intron regions) have some regulatory roles, may be on the same gene or other genes located elsewhere on the chromosome. For example intron 3 of gene A may act as an enhancer sequence of gene B located 500 bp downstream of gene A

In this case the operon is producing three different proteins, if there were no gaps then a fusion protein may have been produced which is not desired

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  • $\begingroup$ Introns, enhancers, what are you going on about? This is a question about prokaryotes. $\endgroup$ – swbarnes2 Oct 3 '18 at 18:23
  • $\begingroup$ I think I clearly mentioned about I am not talking about lac operon, I just explained what the roles of non coding DNAs may be. My bad if my answer sounded otherwise $\endgroup$ – Anindya Oct 3 '18 at 18:41

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