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J Biol Chem. 2014 Dec 19;289(51):35124-38. doi: 10.1074/jbc.M114.612663. Epub 2014 Oct 28.

Argonaute proteins affect siRNA levels and accumulation of a novel extrachromosomal DNA from the Dictyostelium retrotransposon DIRS-1.

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From the Department of Genetics, FB10, Kassel University, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany.
Research Center for Infectious Diseases (ZINF), University of Würzburg, Josef-Schneider-Strasse 2/Bau D15, 97080 Würzburg, Germany, and.
Ribogenetics Biochemistry Laboratory, School of Engineering and Science, Molecular Life Sciences Research Center, Jacobs University, Campus Ring 1, DE-28759 Bremen, Germany.
From the Department of Genetics, FB10, Kassel University, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany,


The retrotransposon DIRS-1 is the most abundant retroelement in Dictyostelium discoideum and constitutes the pericentromeric heterochromatin of the six chromosomes in D. discoideum. The vast majority of cellular siRNAs is derived from DIRS-1, suggesting that the element is controlled by RNAi-related mechanisms. We investigated the role of two of the five Argonaute proteins of D. discoideum, AgnA and AgnB, in DIRS-1 silencing. Deletion of agnA resulted in the accumulation of DIRS-1 transcripts, the expression of DIRS-1-encoded proteins, and the loss of most DIRS-1-derived secondary siRNAs. Simultaneously, extrachromosomal single-stranded DIRS-1 DNA accumulated in the cytoplasm of agnA- strains. These DNA molecules appear to be products of reverse transcription and thus could represent intermediate structures before transposition. We further show that transitivity of endogenous siRNAs is impaired in agnA- strains. The deletion of agnB alone had no strong effect on DIRS-1 transposon regulation. However, in agnA-/agnB- double mutant strains strongly reduced accumulation of extrachromosomal DNA compared with the single agnA- strains was observed.


Argonaute; Gene Silencing; RNA Interference (RNAi); Small Interfering RNA (siRNA); Transposable Element (TE)

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