NatA acetyltransferase

NatA acetyltransferase(N^α acetyltransferase), is an enzyme that serves to catalyze the addition of acetyl groups to various proteins emerging from the ribosome. Upon translation, the NatA binds to the ribosome and then "stretches" to the front end of the forming, or nascent, polypeptide, where it adds this acetyl group. This acetyl group is added to the front end, or N-terminus of the new protein.

Forty percent of all proteins in the yeast proteome are thought to be N-terminally acetylated, with a corresponding figure of 90% in mammalian proteins.^[1]

To be specific, NatA is the main N{alpha}-terminal acetyltransferase in the yeast cytosol, responsible for the acetylation of proteins at locations in which L-serine, L-alanine, L-threonine, or glycine are present.^[2][3]

NatA Acetyltransferase is not a single protein but a complex of three subunits.

Sup35p acetylation

In Saccharomyces cerevisiae NatA acetyltransferase interacts with the Sup35p protein. It is involved in the reaction of the [PSI+], converting the [psi-] to its own conformation. Thus, [PSI+] strains deficient in NatA Acetyltransferase have been found to have an altered interaction between Sup35p[PSI+] and nascent Sup35p. This interaction at the post-translational level still produces a prion with classical beta sheets, but this version of the interaction does not take away the function of this third release factor. Thus, stop codons are translated reliably in [PSI+] strains lacking NatA Acetyltransferase.^[4]

Subunits in yeast

• Nat1p – 98kDa, functions to bind to anchor onto the ribosome
• Ard1p – 27kDA, has catalytic properties which acetylate the nascent polypetide.
• Nat5p – Newly discovered, unknown function.

Yeast cells lacking Natp and Ard1p show a reduced sporulation efficiency, failure to enter G₀ phase under specific conditions, defect in silencing of the silent mating-type loci, and decreased survival after heat shock. However, strains lacking Nat5p do not show any obvious difference to the phenotype.

Comparisons

Natp requires longer nascent polypeptide chains to function catalystically than NAC (nascent polypeptide-associated complex) and Hsp70 homologue Ssb1/2p.

References

1. Caesar, Robert, Jonas Warringer, and Anders Blomberg. "Physiological Importance and Identification of Novel Targets for the N-Terminal Acetyltransferase NatB – Caesar et al. 5 (2): 368 --." Eukaryotic Cell. 16 December 2005. Web. 31 January 2010. <http://ec.asm.org/cgi/content/full/5/2/368>.
2. Gautschi, Matthias, Sören Just, Andrej Mun, Suzanne Ross, Peter Rücknagel, Yves Dubaquié, Ann Ehrenhofer-Murray, and Sabine Rospert. "The Yeast N{alpha}-Acetyltransferase NatA Is Quantitatively Anchored to the Ribosome and Interacts with Nascent Polypeptides." (2003). Molecular and Cellular Biology. Web. 22 January 2010. <http://mcb.asm.org/cgi/content/full/23/20/7403>.
3. Polevoda, Bogdan, Jason Hoskins, and Fred Sherman. "Properties of Nat4, an N{alpha}-Acetyltransferase of Saccharomyces cerevisiae That Modifies N Termini of Histones H2A and H4 – Polevoda et al. 29 (11): 2913 --." Molecular and Cellular Biology. Web. 25 January 2010. <http://mcb.asm.org/cgi/content/full/29/11/2913>.
4. "The NatA Acetyltransferase Couples Sup35 Prion Complexes to the [PSI ] Phenotype – Pezza et al. 20 (3): 1068– ." Molecular Biology of the Cell. (2008) <http://www.molbiolcell.org/cgi/content/full/20/3/1068>.