RESUMO
Attenuation of pre-rRNA synthesis in response to elevated temperature is accompanied by increased levels of PAPAS ("promoter and pre-rRNA antisense"), a long noncoding RNA (lncRNA) that is transcribed in an orientation antisense to pre-rRNA. Here we show that PAPAS interacts directly with DNA, forming a DNA-RNA triplex structure that tethers PAPAS to a stretch of purines within the enhancer region, thereby guiding associated CHD4/NuRD (nucleosome remodeling and deacetylation) to the rDNA promoter. Protein-RNA interaction experiments combined with RNA secondary structure mapping revealed that the N-terminal part of CHD4 interacts with an unstructured A-rich region in PAPAS. Deletion or mutation of this sequence abolishes the interaction with CHD4. Stress-dependent up-regulation of PAPAS is accompanied by dephosphorylation of CHD4 at three serine residues, which enhances the interaction of CHD4/NuRD with RNA and reinforces repression of rDNA transcription. The results emphasize the function of lncRNAs in guiding chromatin remodeling complexes to specific genomic loci and uncover a phosphorylation-dependent mechanism of CHD4/NuRD-mediated transcriptional regulation.
Assuntos
DNA Ribossômico/genética , Regulação da Expressão Gênica/genética , Temperatura Alta , Regiões Promotoras Genéticas/genética , RNA Longo não Codificante/metabolismo , RNA Ribossômico/genética , Estresse Fisiológico/genética , Animais , Elementos Facilitadores Genéticos , Células HEK293 , Humanos , Complexo Mi-2 de Remodelação de Nucleossomo e Desacetilase/metabolismo , Camundongos , Células NIH 3T3 , Fosforilação , Estrutura Secundária de Proteína , RNA Ribossômico/biossínteseRESUMO
The maintenance of eukaryotic genome stability is ensured by the interplay of transcriptional as well as post-transcriptional mechanisms that control recombination of repeat regions and the expression and mobility of transposable elements. We report here that mutations in two (cytosine-5) RNA methyltransferases, Dnmt2 and NSun2, impact the accumulation of mobile element-derived sequences and DNA repeat integrity in Drosophila. Loss of Dnmt2 function caused moderate effects under standard conditions, while heat shock exacerbated these effects. In contrast, NSun2 function affected mobile element expression and genome integrity in a heat shock-independent fashion. Reduced tRNA stability in both RCMT mutants indicated that tRNA-dependent processes affected mobile element expression and DNA repeat stability. Importantly, further experiments indicated that complex formation with RNA could also contribute to the impact of RCMT function on gene expression control. These results thus uncover a link between tRNA modification enzymes, the expression of repeat DNA, and genomic integrity.