NAT2, an essential gene encoding methionine N alpha-acetyltransferase in the yeast Saccharomyces cerevisiae

N alpha-Acetylation is catalyzed by N alpha-acetyltransferases, which transfer acetyl groups from acetyl coenzyme A to the N termini of most eukaryotic proteins co-translationally. NAT1 and ARD1 from the yeast Saccharomyces cerevisiae (Mullen, J. R., Kayne, P. S., Moerschell, R. P., Tsunasawa, S., Gribskov, M., Colavito-Shepanski, M., Grunstein, M., Sherman, F., and Sternglanz, R. (1989) EMBO J. 8, 2067-2075) were previously shown to encode the major N alpha-acetyltransferase, which act on certain proteins having serine, glycine, and alanine but not methionine termini (Sherman, F., Moerschell, R. P., Tsunasawa, S., and Sternglanz, R. (1993) in Methods in Protein Sequence Analysis (Imahori, K., and Sakiyama, F., eds) pp. 173-181, Plenum Publishing Corp., New York). We have identified a second gene, NAT2, that may correspond to the N alpha-acetyltransferase acting on a subset of proteins having methionine termini. Crude extracts of a series of heat-sensitive mutants (Ts-) were screened for acetylation of a 24-amino acid synthetic peptide Met-Asn-Asn- in vitro. One mutant, nat2-1, out of 115 strains examined, lacked acetyltransferase activity, and the mutation co-segregated as a single gene with the heat-sensitive phenotype. The nat2-1 mutants were deficient in the ability to acetylate Met-Asn-Asn- and Met-Glu-Arg-peptides but were able to N alpha-acetylate Ser-Glu-Phe- and Ser-Tyr-Ser- peptides in vitro. The NAT2 wild-type gene was cloned by complementation of the nat2-1 mutant, and the DNA sequence revealed an open reading frame of 288 amino acids. Gene disruption demonstrated that NAT2 is an essential gene, and hybridization analysis indicated that it is located on chromosome VII. Furthermore, there was limited, but significant identities between the yeast N alpha-acetyltransferases Nat1, Ard1, Nat2, and Mak3, although no common motifs could be identified. We propose that NAT2 encodes the major N alpha-acetyl-transferase acting on certain proteins with only methionine termini, and that N alpha-acetylation of some of these proteins is essential for viability.