Silencing in Triplicate

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Science  06 Oct 2006:
Vol. 314, Issue 5796, pp. 21
DOI: 10.1126/science.314.5796.21b

The movement and activity of transposons, also known as jumping genes for their ability to replicate and move throughout the genome, have long fascinated biologists. In some cases, transposon activity is reduced, and more recently it has been demonstrated that this reduction is often due to epigenetic silencing and paramutation: the epigenetic change in expression of one allele effected by another.

Woodhouse et al. propose that the establishment, maintenance, and inheritance silencing of the MuDR transposon in maize are due to multiple genes. These genes include Mu killer, a transcribed template for RNA interference silencing that initiates silencing; a homolog of the Arabidopsis RDR2 gene, named ZmRDR2/Mediator of paramutation 1, which is required to initiate silencing in the cases where a double-stranded RNA hairpin is lacking and perpetuates silencing through RNA-directed DNA methylation; and two maize homologs of nucleosome assembly protein 1, which maintain heritable silencing, most likely by modification of the chromatin structure. The redundant mechanisms involved in regulating transposon activity demonstrate the importance of controlling the replication of parasitic DNA elements within the host genome, which has been suggested as the raison d'être for epigenetic silencing. — LMZ

PLoS Biol. 4, e339 (2006).

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