Kozak and IRES sequnces same thing?
jzsmith at ucdavis.edu
Fri Nov 7 12:04:17 EST 1997
gj at nospampobox4.stanford.edu wrote:
> Hi, I work on IRESes the major difference between kozak consensus, i.e.
> cap-dependent initiation, and an IRES, i.e. cap independent initiation
> is that the former required eif4e and a cap while cap independent
> initiaion does require either.
This may not be entirely true. While it is clear that cap-independent
initiation of translation does occur in picornavirus infected cells, which
inactivate the p220 component of eIF4E, that does not mean that the
components themselves play no role in the initiation event.
> Interesting IRES mediated initiation
> requires all the other initatiation factors. they cannot substitute for
> one another as a previous poster states kozak sequence is the sequence
> around the AUG while an IRES is more like a cap.
> They do not do the same thing. Kozak sequence denotes the start codon,
> while an IRES element recuits the ribosome(43S) to the mRNA. Some IRES
> elements recuit the ribosome directly to the start codon (typeII) while
> others recuit the ribosome to the mRNA. The ribosome than scans to the
> start codon using convential scanning mechanism. In addition there are a
> few cellular IRES containing mRNAs. Hope this answers your questions
> Gregg email not valid
Some cellular mRNAs thought to be capable of cap-indenpendent translation
are grp78/BiP (Macejak and Sarnow) and antennapedia from Dros. (Oh and
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