Nuclear RNA-acetylation can be erased by the deacetylase SIRT7

A large number of RNA modifications are known to affect processing and function of rRNA, tRNA and mRNA 1. The N4-acetylcytidine (ac4C) is the only known RNA acetylation event and is known to occur on rRNA, tRNA and mRNA 2,3. RNA modification by acetylation affects a number of biological processes, including translation and RNA stability 2. For a few RNA methyl modifications, a reversible nature has been demonstrated where specific writer proteins deposit the modification and eraser proteins can remove them by oxidative demethylation 4-6. The functionality of RNA modifications is often mediated by interaction with reader proteins that bind dependent on the presence of specific modifications 1. The NAT10 acetyltransferase has been firmly identified as the main writer of acetylation of cytidine ribonucleotides, but so far neither readers nor erasers of ac4C have been identified 2,3. Here we show, that ac4C is bound by the nucleolar protein NOP58 and deacetylated by SIRT7, for the first time demonstrating reversal by another mechanism than oxidative demethylation. NOP58 and SIRT7 are involved in snoRNA function and pre-ribosomal RNA processing 7-10, and using a NAT10 deficient cell line we can show that the reduction in ac4C levels affects both snoRNA sub-nuclear localization and pre-rRNA processing. SIRT7 can deacetylate RNA in vitro and endogenous levels of ac4C on snoRNA increase in a SIRT7 deficient cell line, supporting its endogenous function as an RNA deacetylase. In summary, we identify the first eraser and reader proteins of the RNA modification ac4C, respectively, and suggest an involvement of RNA acetylation in snoRNA function and pre-rRNA processing.