Details
of
chain
initiation
and
of
the
components
of
the
synthetic
apparatus
in
eukaryotic
cells.
The
initiation
process
involves
the
ordered
formation
of
complexes
among
an
initiation
factor
protein
(eIF2),
GTP,
the
initiating
methionyl-tRNA
(met-tRNA),
and
the
small
(40S)
ribosomal
subunit.
This
complex,
along
with
other
initiation
factors,
binds
to
the
5'-end
of
an
mRNA
and
then
moves
along
the
mRNA
until
it
reaches
the
first
AUG
codon.
(This
is
in
contrast
to
the
prokaryotic
system,
in
which
the
ribosome-tRNA
complex
binds
directly
to
the
AUG
codon.)
The
large
(60S)
ribosome
subunit
joins
the
complex
along
with
the
hydrolysis
of
the
GTP
and
the
release
of
initiation
factors.
The
met-tRNA
used
in
initiation
is
specific
for
this
step
and
does
not
participate
in
the
positioning
of
other
methionine
residues
in
the
polypeptide
chain.
However,
in
contrast
to
prokaryotes,
the
eukaryotic
initiator
methionine
is
not
formulated.
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