Page 100 - Academic Press Encyclopedia of Physical Science and Technology 3rd Molecular Biology

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Encyclopedia of Physical Science and Technology EN017F-788 August 3, 2001 16:27

Translation of RNA to Protein 41

FIGURE 8 Schematic diagram illustrating the formation of initiation complexes. (a) Prokaryotic initiation. The following
symbols are used for initiation factors and other components involved in the formation of the 70S initiation complex:
, IF-1; , IF-2; , IF-3; , fMet-tRNA f , , GTP; other symbols are defined in the figure. (b) Eukaryotic initiation
complexes in mammalian protein biosynthesis from components defined in the figure. The process may be divided
into three stages: a, formation of a 43S pre-initiation complex; b, binding of mRNA with formation of a 48S pre-initiation
complex; and c, synthesis of the 80S initiation complex containing the initiator tRNA in the correct position for peptide
bond formation. [From Arnstein, H. R. V., and Cox, R. A. (1992). “Protein Biosynthesis,” Oxford University Press,
Oxford. With permission.]

of the Met-tRNA Met . However, this recognition also de- sequence context is unfavorable, initiation becomes ineffi-
f
pends in some way on eIF-2 and may be modulated as a cient, hence most 40S subunits will tend to initiate further
result of deviation of the mRNA structure from the consen- along the mRNA at another AUG triplet in a more favor-
A
sus sequence GCCGCC / G CCAUGG. Sequence context able context. This model also explains rare cases where
may also account for the rare cases where initiation occurs initiation is not restricted to one particular AUG codon and
downstream of the 5 -proximal AUG codon. Where this translation of a single mRNA gives rise to two proteins.