The Yeast N super( alpha )-Acetyltransferase NatA Is Quantitatively Anchored to the Ribosome and Interacts with Nascent Polypeptides

• Published in: Molecular and cellular biology Vol. 23; no. 20; pp. 7403 - 7414
• Main Authors: Gautschi, M, Just, S, Mun, A, Ross, S, Ruecknagel, P, Dubaquie, Y, Ehrenhofer-Murray, A, Rospert, S
• Format: Journal Article
• Language: English
• Published: 01.10.2003
• ISSN: 0270-7306
• DOI: 10.1128/MCB.23.20.7403-7414.2003

The majority of cytosolic proteins in eukaryotes contain a covalently linked acetyl moiety at their very N terminus. The mechanism by which the acetyl moiety is efficiently transferred to a large variety of nascent polypeptides is currently only poorly understood. Yeast N super( alpha )-acetyltransferase NatA, consisting of the known subunits Nat1p and the catalytically active Ard1p, recognizes a wide range of sequences and is thought to act cotranslationally. We found that NatA was quantitatively bound to ribosomes via Nat1p and contained a previously unrecognized third subunit, the N super( alpha ) -acetyltransferase homologue Nat5p. Nat1p not only anchored Ard1p and Nat5p to the ribosome but also was in close proximity to nascent polypeptides, independent of whether they were substrates for N super( alpha )-acetylation or not. Besides Nat1p, NAC (nascent polypeptide-associated complex) and the Hsp70 homologue Ssb1/2p interact with a variety of nascent polypeptides on the yeast ribosome. A direct comparison revealed that Nat1p required longer nascent polypeptides for interaction than NAC and Ssb1/2p. [Delta] nat1 or [Delta] ard1 deletion strains were temperature sensitive and showed derepression of silent mating type loci while [Delta] nat5 did not display any obvious phenotype. Temperature sensitivity and derepression of silent mating type loci caused by [Delta] nat1 or [Delta] ard1 were partially suppressed by overexpression of SSB1. The combination of data suggests that Nat1p presents the N termini of nascent polypeptides for acetylation and might serve additional roles during protein synthesis.