ARD1 and NAT1 proteins form a complex that has N-terminal acetyltransferase activity

Two yeast genes, ARD1 and NAT1, are required for the expression of an N-terminal protein acetyltransferase. This activity is required for full repression of the silent mating type locus HML, for sporulation, and for entry into G0. While the NAT1 gene product is thought to be the catalytic subunit of the enzyme, the role of the ARD1 protein has remained unclear. We have used epitope tagged derivatives of ARD1 and NAT1 to provide biochemical evidence for the formation of an ARD1-NAT1 complex, and to show that both proteins are required for the N-terminal acetyltransferase activity. We also present evidence for the formation of ARD1-ARD1 homodimers. Deletion analysis suggests that the C-terminal region of ARD1 may be involved in the formation of both ARD1-ARD1 and ARD1-NAT1 complexes.