Molecular Genetics

One biotechnological technique for correcting mutations is chimeroplasty, a method the likely uses DNA repair processes.

Facts

• Molecules that are part RNA and part DNA (chimeras) and whose RNA part is complementary to the DNA part can be synthesized.
• Molecules in which the RNA: DNA hybrid portion is that of a target gene except for one position may be useful in introducing point substitutions into genomes in living cells. At the exceptional position, the molecule has a mismatch representing the desired nucleotide change.
• Cultured tobacco cells containing a green fluorescent protein (GFP) gene that has been inactivated by a point mutation were treated with a chimera for the GFP gene with a mismatch at the inactivating mutation position.
• After treatment, a proportion of the cultured cells became green fluorescent.

Interpretations

• RNA-DNA chimeras, such as those described, stimulate a process resulting in alteration of specific nucleotides in genomes.
• The technique can be used to:
  • correct deleterious mutations;
  • introduce novel beneficial mutations
• How this technique, called chimeroplasty, works is not immediately obvious.

Further information

• Preliminary evidence indicates that DNA mismatch repair may be responsible for the chimera-induced substitutions. Recombination had originally been implicated but has since been shown not to be responsible.
• Other changes reported to be accomplished by chimeroplasty include:
  • conversion of the acetolactate synthase gene to a form for a sufonylurea herbicide resistant enzyme;
  • correction of the sickle cell anemia defect in hemoglobin;
  • activation of the c-ras oncogene;
  • conversion of albino cells to melanin-synthesizing cells.
• The technique is, at present, reproducible with variable efficiency. How many non-specific changes, if any, are induced by the chimeroplasty is not known. Thus, widespread biotechnological use is not imminent.
• Oligonucleotides that form triple-helical structures with target sequences have been shown to induce mutations in their targets ( ref )

This is page 31341 of Molecular Genetics by Ulrich Melcher , © 1999, 2000