1. Molecular Mechanism of
antisense molecules
By
Prabhu Thirusangu,
Molecular Biomedicine Laboratory,
Sahyadri Science College,
Kuvempu University
2. What is Antisense RNA?
• Antisense RNA is a single-stranded RNA that is complementary to a
messenger RNA (mRNA) strand transcribed within a cell.
• Antisense RNA may be introduced into a cell to inhibit translation of a
complementary mRNA by base pairing to it and physically obstructing the
translation machinery.
3. In the Past…
• Historically, the effects of antisense RNA have often been confused with
the effects of RNA interference (RNAi).
• RNA interference is a related process in which double-stranded RNA
fragments called small interfering RNAs trigger catalytically mediated gene
silencing, most typically by targeting the RNA-induce silencing complex
(RISC) to bind to and degrade the mRNA.
• Attempts have been made to genetically engineer transgenic plants to
express antisense RNA instead to activate the RNAi pathway.
• Well-known examples include the Flavr Savr tomato and two cultivars of
ringspot-resistant papaya
4. Molecular Mechanism
Messenger RNA – An Introduction
• Messenger RNA (mRNA) is single-stranded.
• Its sequence of nucleotides is called "sense" because it results
in a gene product (protein).
• Normally, its unpaired nucleotides are "read" by transfer RNA
anticodons as the ribosome proceeds to translate the
message.
6. RNA can Mimic DNA!!!
• RNA can form duplexes just as DNA does.
• All that is needed is a second strand of RNA whose sequence of bases is
complementary to the first strand; e.g.,
5´ C A U G 3´ mRNA
3´ G U A C 5´ Antisense RNA
• The second strand is called the antisense strand because its sequence of
nucleotides is the complement of message sense.
7. Blocking Translation
• When mRNA forms a duplex with a complementary antisense RNA
sequence, translation is blocked.
This may occur because
1. The ribosome cannot gain access to the nucleotides in the mRNA or
2. Duplex RNA is quickly degraded by ribonucleases in the cell.
11. Applications
Flavr Savr Tomato
• Ethylene synthesized by the tomato causes them to ripen and spoil before
they reach the customer.
• Transgenic tomatoes have been constructed that carry in their genome an
artificial gene (DNA) that is transcribed into an antisense RNA
complementary to the mRNA for an enzyme involved in ethylene
production. These tomatoes make only 10% of the normal amount of the
enzyme.
12. Antisense RNA also occurs naturally
Do Cells naturally block the translation?
• The answer is yes, and these seem to represent another method of regulating
gene expression.
• In both mice and humans, the gene for the insulin-like growth factor 2 receptor
(Igf2r) that is inherited from the father synthesizes an antisense RNA that appears
to block synthesis of the mRNA for Igf2r.
13. Conclusion
Antisense RNA has long been thought of as a promising technique for
disease therapy; the only such case to have reached the market is the drug
fomivirsen.
One commentator has characterized antisense RNA as one of
“Dozens of technologies that are gorgeous in
concept, but exasperating in commercialization"
Generally, antisense RNA still lack effective design, biological activity, and
efficient route of administration.
