NatA Acetyltransferase
Encyclopedia
NatA 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.
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.
In addition, the enzyme can be classified as an epigenic factor, because it has been found to acetylate histones as well.
NatA Acetyltransferase is not a single protein but a complex of three subunits.
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.
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.
homologue Ssb1/2p.
Acetyl
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...
groups to various proteins emerging from the ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
. 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.
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
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
, L-alanine
Alanine
Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
, L-threonine
Threonine
Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
, or glycine
Glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...
are present.
In addition, the enzyme can be classified as an epigenic factor, because it has been found to acetylate histones as well.
NatA Acetyltransferase is not a single protein but a complex of three subunits.
Sup35p Acetylation
In Saccharomyces cerevisiaeSaccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
NatA Acetyltransferase interacts with the Sup35p
Sup35p
Sup35p is the Saccharomyces cerevisiae eukaryotic translation release factor. More specifically, it is the yeast eukaryotic release factor 3 , which forms the translation termination complex with eRF1 . This complex recognizes and catalyzes the release of the nascent polypeptide chain when the...
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
Release factor
A release factor is a protein that allows for the termination of translation by recognizing the termination codon or stop codon in a mRNA sequence....
. Thus, stop codons are translated reliably in [PSI+] strains lacking NatA Acetyltransferase.
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
G0 phase
The G0 phase is a period in the cell cycle in which cells exist in a quiescent state. G0 phase is viewed as either an extended G1 phase, where the cell is neither dividing nor preparing to divide, or a distinct quiescent stage that occurs outside of the cell cycle...
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 Hsp70Hsp70
The 70 kilodalton heat shock proteins are a family of ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms...
homologue Ssb1/2p.