Kozak and IRES sequnces same thing?
kay at lyon151.inserm.fr
Wed Nov 5 06:03:39 EST 1997
In article <345FE918.851A796B at cyllene.uwa.edu.au>, mwatson at cyllene.uwa.edu.au
>I am wondering what the differnce in function is between a Kozak
>sequence and an Internal Ribosome Entry Site (IRES). Does anyone know?
>Do they do the same thing? can one substitute for another?
The answer to whether they are the same thing is no. The Kozak sequence
defines a consensus sequence around an ATG codon which provides a good
environement for the ATG codon to function as the translational initiation
codon. Normally, a ribosome will attach to an mRNA 5' cap structure and then
scan down the RNA until it encounters a suitable ATG codon, usually but not
always in a Kozak environement, and then starts translation. When an IRES is
used, the ribosome will attach directly to this internal structure (cap
independant attachment), and then scan down until it finds a favourable ATG
initiation codon. The IRES will therefore still need a good initiation codon
(Kozak sequence usually) downstream, but a Kozak sequence does not
necessarily need an IRES.
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