Importance of the Sir3 N terminus and its acetylation for yeast transcriptional silencing

The N-terminal alanine residues of the silencing protein Sir3 and of Orc1 are acetylated by the NatA Nalpha-acetyltransferase. Mutations demonstrate that the N terminus of Sir3 is important for its function. Sir3 and, perhaps, also Orc1 are the NatA substrates whose lack of acetylation in ard1 and nat1 mutants explains the silencing defect of those mutants.