Kozak and IRES sequnces same thing?

gj at nospampobox4.stanford.edu gj at nospampobox4.stanford.edu
Wed Nov 5 13:15:45 EST 1997

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. 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

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