top1 and sir2 share silencing loss and H4K16 hyperacetylation at rDNA. Top1p recruits Sir2p to ribosomal genes by interacting with its N-terminal domain. Top1p–Sir2p interaction justifies shared rDNA phenotypes. The Sir2p–Top1p interaction does not require Topo1 catalytic activity. New role for Topo1 as scaffold protein for molecular interactions