Unformatted text preview: n: The Preinitiation Complex
Translation initiates with the formation of a
preinitiation complex consisting of the
messenger RNA, a 30S ribosomal subunit and
a special aminoacyl-tRNA molecule, tRNAf-met.
Bacterial protein synthesis initiates with Nformyl methionine at a methionine codon,
(AUG) near the 5' end of the mRNA.
Initiation factors 1 and 3 (IF1 and IF3) bind to
the 30S subunit and block the binding of the
The anticodon of tRNAf-met base pairs with the
initiation codon on the mRNA.
IF2 binds to tRNAf-met and brings it to the 30S
subunit. Once the tRNAf-met is bound to the 30S
subunit, IF2 hydrolyzes GTP, causing the
dissociation of IF1, IF2, and IF3.
The 50S subunit contains three sites, E (exit),
P (peptidyl) site and an A (aminoacyl) site. In
the 70S initiation complex the tRNAf-met lies in
the peptidyl site.
IF3 + IF1
+ IF3 IF3 IF1 IF1 IF3 IF1 IF3
IF1 BIS101001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013...
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