Everything about The Shine-dalgarno Sequence totally explained
The
Shine-Dalgarno sequence (or Shine-Dalgarno box), proposed by
Australian scientists
John Shine and
Lynn Dalgarno, is a
ribosomal binding site generally located 6-7 nucleotides upstream of the
start codon AUG. The Shine-Dalgarno sequence exists only in
prokaryotes; the six-base
consensus sequence is
AGGAGG. This sequence helps recruit the ribosome to the
mRNA to initiate
protein synthesis by aligning it with the
start codon. The complementary sequence (
CCUCCU), is called the
anti-Shine-Dalgarno sequence and is located at the 3' end of the
16S rRNA in the ribosome. The eukaryotic equivalent of the Shine-Dalgarno sequence is called the
Kozak sequence. The Shine-Dalgarno sequence in E. coli, for example, is AGGAGGA.
Mutations in the Shine-Dalgarno sequence can reduce
translation. This reduction is due to a reduced mRNA-ribosome pairing efficiency, as evidenced by the fact that complementary mutations in the anti-Shine-Dalgarno sequence can restore translation.
When the Shine-Dalgarno sequence and the anti-Shine-Dalgarno sequence pair, the translation
initiation factors
IF2-GTP,
IF1,
IF3, as well as the initiator tRNA
fMet-tRNA(fMET) are recruited to the ribosome.
Shine-Dalgarno sequence vs. ribosomal S1 protein
In
Gram-negative bacteria, however, Shine-Dalgarno sequence presence isn't obligatory for ribosome to locate initiator codon, since deletion of Anti-Shine-Dalgarno sequence from
16S rRNA doesn't lead to translation initiation at non-authentic sites. Moreover, numerous prokaryotic mRNAs don't possess Shine-Dalgarno sequences at all. What principally attracts ribosome to mRNA initiation region is apparently ribosomal protein S1, which binds to AU-rich sequences found in many prokaryotic mRNAs 15-30 nucleotides upstream of start-codon. It should be noted, that S1 is only present in
Gram-negative bacteria, being absent from
Gram-positive species.
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