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EMBO Rep. 2008 Aug;9(8):774-80. doi: 10.1038/embor.2008.109. Epub 2008 Jul 4.

The structure of NoRC-associated RNA is crucial for targeting the chromatin remodelling complex NoRC to the nucleolus.

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Division of Molecular Biology of the Cell II, German Cancer Research Center, DKFZ-ZMBH-Alliance, INF 581, D-69120 Heidelberg, Germany.


Silencing of ribosomal RNA genes (rDNA) requires binding of the chromatin remodelling complex NoRC to RNA that is complementary to the rDNA promoter. NoRC-associated RNA (pRNA) folds into a conserved stem-loop structure that is required for nucleolar localization and rDNA silencing. Mutations that disrupt the stem-loop structure impair binding of TIP5, the large subunit of NoRC, to pRNA and abolish targeting of NoRC to nucleoli. Binding to pRNA results in a conformational change of TIP5, as shown by enhanced sensitivity of TIP5 towards trypsin digestion. Our results indicate an RNA-dependent mechanism that targets NoRC to chromatin and facilitates the interaction with co-repressors that promote heterochromatin formation and rDNA silencing.

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