NAT2, AN ESSENTIAL GENE ENCODING METHIONINE N-ALPHA-ACETYLTRANSFERASEIN 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 pre viously shown to encode the major N-alpha-acetyltransferase, which act on certain proteins having serine, glycine, and alanine but not methi onine termini (Sherman, F., Moerschell, R. P., Tsuna sawa, S., and Ste rnglanz, R. (1993) in Methods in Protein Sequence Analysis (Imahori, K ., and Sakiyama, F., eds) pp. 173-181, Plenum Publishing Corp., New Yo rk). We have identified a second gene, NAT2, that may correspend to th e N-alpha-acetyltransferase acting on a subset of proteins having meth ionine termini. Crude extracts of a series of heat-sensitive mutants ( Ts(-)) were screened for acetylation of a 24-amino acid synthetic pept ide Met-Asn-Asn- in vitro. One mutant, nat2-1, out of 115 strains exam ined, lacked acetyltransferase activity, and the mutation co segregate d as a single gene with the heat-sensitive phenotype. The nat2-1 mutan ts 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 comp lementation of the nat2-1 mutant, and the DNA sequence revealed an ope n reading frame of 288 amino acids. Gene disruption demonstrated that NAT2 is an essential gene, and hybridization analysis indicated that i t is located on chromosome VII. Furthermore, there was limited, but si gnificant 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 act ing on certain proteins with only methionine termini, and that N-alpha -acetylation of some of these proteins is essential for viability.