string: H4K16ac - recognized by TIP5 at the Pol I promoter represses pre-rRNA genes through a NoRC-dependent chromatin-silencing mechanism (Strohner et al., 2001; Zhou and Grummt, 2005), which is critical to decreasing energy expenditure and protecting cells from apoptosis during energy deprivation (Grummt and Ladurner, 2008).