Electronic Journal of Biotechnology ISSN: 0717-3458
  © 2004 by Universidad Católica de Valparaíso -- Chile
Vol. 7 No. 3, Issue of December 15, 2004


Figure 5. Mechanistic model for PTGS. The presence of multiple transgenic copies can lead to epigenetic modifications that could interfere with normal transcription resulting in the production of single-stranded RNA molecules, called aberrant RNA (asRNA). These RNA molecules when exported into the cytoplasm are recognized as a template by RdRPs and short antisense RNA molecules are polymerized. Alternatively, antisense RNA could result from the processing - possibly operated by MUT7- of large dsRNA molecules, formed by RdRP on single-stranded aberrant RNA. Small antisense RNA could then interact with homologous mRNA leading to the degradation of the single stranded portion of the RNA hybrid. Alternatively, small antisense RNAs could act as primers for an RdRP which produces large dsRNA molecules that are eventually degraded, leading to the accumulation of additional antisense RNA, thus creating a catalytic loop. Moreover, dsRNA molecules or even asRNAs could enter into the nucleus and interact with homologous transgenes inducing epigenetic changes necessary for the maintenance of gene silencing.

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