Poster abstracts

Poster number 65 submitted by Meng Sun

A novel repeated RNA/DNA-binding motif in Argonaute proteins

Meng Sun (Department of Chemistry and Biochemistry, The Ohio State University, Columbus OH 43210), Kotaro Nakanishi (Department of Chemistry and Biochemistry, The Ohio State University, Columbus OH 43210)

Abstract:
RNA interference (RNAi) is a eukaryote-specific phenomenon to degrade target RNAs by small noncoding RNAs. To this end, these small RNAs are loaded onto Argonaute (AGO) proteins to form a ribonucleoprotein. RNAi pathway was discovered in some budding yeasts such as Saccharomyces castellii along with non-canonical Dicer, though it is to be noted that Saccharomyces cerevisiae, a model budding yeast, yet lacks RNAi (1, 2). Recently, we revealed that S. castelli Argonaute (ScasAGO) possesses another RNA binding region - extended N-terminal domain (exN), in addition to well-characterized MID and PAZ domains responsible for the guide RNA binding at the 5’ and 3’ termini, respectively. The exN domain also exists in AGO proteins from some other species including plants, but is not found in human and flies. Here we report that the exN domain retains a DNA-binding activity as well. We also discovered that the exN domain consists of seven lysine-rich regions (K-clusters) with the consensus sequence K-xKKxKKxKxKKxK (x represents any amino acid) spaced by linkers of a similar sequence. This is, by far, a novel repeated RNA/DNA-binding motif that is reported for the first time. This K-cluster is found in several proteins including H1 histone proteins, which bind the linker DNA between nucleosomes. Given a recent report that H1 recruits another RNA silencing complex Piwi-piRNA to target loci to silence transposons in the nucleus (Siomi et. el, Keystone Symposium abstract 3005, unpublished data), we surmise that ScasAGO plays an unidentified role in the nucleus, tethering its exN to the nucleosome.

1. Drinnenberg IA, Weinberg DE, Xie KT, Mower JP, Wolfe KH, Fink GR, Bartel DP. 2009. RNAi in budding yeast. Science 326:544-550.
2. Weinberg DE, Nakanishi K, Patel DJ, Bartel DP. 2011. The inside-out mechanism of Dicers from budding yeasts. Cell 146:262-276.


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