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The Wikipedia entry for Gene contains the statement:

The transcribed pre-mRNA contains untranslated regions at both ends which contain a ribosome binding site, terminator and start and stop codons.

But the page on the Start codon says:

The start codon is often preceded by a 5' untranslated region (5' UTR)

So is the start codon a part of the UTR?

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Because the start codon is translated into methionine, it clearly can not be part of the 5'-untranslated region, as @Johnny writes in his answer.

The more contentious question would be for the stop codons and the 3'-untranslated region. Then it really is a question of semantics. One might argue that as no amino acid is inserted in response to these codons, they are not translated. However if one considers the meaning of the word ‘translate’ and its application to the genetic code, a stop codon clearly is translated — it is read and translated into information which initiates the release of the nascent peptide from the ribosome.

And so in the Wikipedia entry on Untranslated Regions it (together with the start codon) is shown in the coding sequence, and not in the untranslated region. The annotations used by GenBank also include start and stop codons in the coding sequence (CDS in their annotations) — see, for example the annotation for this insulin precursor sequence.

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The start codon both in prokaryotes and eukaryotes isn't a part of the 5'UTRs, it is present downstream the UTRs.

In prokaryotes the Ribosome binds to the Shine-Dalgarno sequence (AGGAGGU) of 5'UTR. This sequence is found 3-10 base pairs upstream from the initiation codon.

In eukaryotes the initiator codon is usually the first 5'AUG3' present on kozak consensus sequence (GCCGCCRCCAUGG, where R is adenine or guanine). The ribosome does not bind to this sequence directly but browsing for it from the 5' end it starts synthesis once it reaches the consensus sequence. This kozak sequence ranges from the terminal portion of 5'UTR to the first few (actually four) nucleotides of translating region.

Sources:

  • Principles of genetics by Snustard and Simmons

  • Berg's Biochemistry

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  • $\begingroup$ That translation starts from the terminal part of the untranslated region seems unsemantic. $\endgroup$ – canadianer Feb 22 '17 at 0:52
  • $\begingroup$ I've updated the answer. $\endgroup$ – Tyto alba Feb 23 '17 at 14:41
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This statement is incorrect.

The transcribed pre-mRNA contains untranslated regions at both ends which contain a ribosome binding site, terminator and start and stop codons.

The start codon always encodes for methionine (eukaryotes) or N-Formylmethionine (prokaryotes), thus, seeing that the start codon encodes an amino acid, it would be considered part of the translating region.

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