Molecular Genetics

One way of connecting points on a molecular map with points on a genetic map is the antisense strategy.

Facts

Endopolygalacturonase of tomato was suspected of having a prominent role in the softening of tomato fruit during ripening. In vitro, a DNA fragment corresponding to part of the endopolygalacturonase gene was inserted next to a transcription promoter in the orientation opposite to the normal orientation. Transcription from this promoter should make RNA complementary to endopolygalacturonase mRNA. Such cRNAs are known as antisense RNAs. The constructed antisense gene was used to transform tomato using Agrobacteria. Antisense transgenic plants produced fruit that softened more slowly than normal fruit (ref).

Interpretations

• The antisense strategy is an alternative to the knock-out strategy, particularly in organisms in which homologous recombination is difficult to achieve.
• Antisense transgenes are usually dominant in their effects.
• If the location of the gene on the molecular map is known, the antisense strategy may associate a genetically scorable phenotype with that map position, thus tying the two types of maps together.
• Antisense strategies should work with multigene families provided the members are sufficiently closely related.

Further information

• The mechanism through which cRNA inhibits processes is not yet clearly understood, but may involve double-stranded RNA-mediated degradation of mRNA.
• Since double-stranded (ds) RNA is often more effective inducing antisense effects, antisense RNA may function solely by forming ds RNA in the organism. The dsRNA appears to induce RNA degradation mechanisms that can last through many cell generations. The phenomenon may be another version of co-suppression.
• Attempts to use antisense strategies for other purposes are made difficult for two reasons (ref).
  • The target sequences are not always available for binding by the antisense molecule.
  • The antisense molecule may have other unexpected effects on the organism.
• Another way of connecting points on a molecular map with points on a genetic map is the knock-out strategy.

This is page 1234 of Molecular Genetics by Ulrich Melcher, © 1997, 1998, 1999, 2000