Molecular Cloning and Sequencing of a cDNA Encoding Nα-Acetyltransferase from Saccharomyces cerevisiae

A novel N(alpha)-acetyl alanine aminopeptidase from Allomyces arbuscula

An N(alpha)-acetyl alanine aminopeptidase has been purified from the aquatic fungus Allomyces arbuscula. The apparent molecular mass of the enzyme was estimated to be 280 kDa by gel filtration through calibrated Sephacryl S300 column. In SDS-PAGE, the purified enzyme appeared as a single band of M(r) 80 kDa. Catalytic activity of the enzyme was inhibited by specific serine protease inhibitors, 3,4-DCI and APMSF, as well as SH reacting compounds, HgCl(2) and iodoacetate, indicating that the enzyme is a serine protease with some functional SH group(s) involved in the catalytic reaction. 3H-DFP was used to label the reactive serine of the enzyme. When the labeled protein was analyzed in SDS-PAGE, most of the label appeared in the M(r) 80 kDa band, however, a few additional faster migrating minor bands were also seen, probably representing a minor degradation product of the enzyme. The enzyme cleaved mainly N(alpha)-acetlylated alanine, although a small but negligible activity was also obtained with acetylated leucine and phenylalanine. The role of the enzyme in N-end rule proteolysis is discussed.

New yeast genes important for chromosome integrity and segregation identified by dosage effects on genome stability

Phenotypes produced by gene overexpression may provide important clues to gene function. Here, we have performed a search for genes that affect chromo-some stability when overexpressed in the budding yeast Saccharomyces cerevisiae. We have obtained clones encompassing 30 different genes. Twenty-four of these genes have been previously characterized. Most of them are involved in chromatin dynamics, cell cycle control, DNA replication or mitotic chromosome segregation. Six novel genes obtained in this screen were named CST (chromosome stability). Based on the pattern of genomic instability, inter-action with checkpoint mutations and sensitivity to chromosome replication or segregation inhibitors, we conclude that overexpression of CST4 specifically interferes with mitotic chromosome segregation, and CST6 affects some aspect of DNA metabolism. The other CST genes had complex pleiotropic phenotypes. We have created deletions of five genes obtained in this screen, CST9, CST13, NAT1, SBA1 and FUN30. None of these genes is essential for viability, and deletions of NAT1 and SBA1 cause chromosome instability, a phenotype not previously associated with these genes. This work shows that analysis of dosage effects is complementary to mutational analysis of chromosome transmission fidelity, as it allows the identification of chromosome stability genes that have not been detected in mutational screens.

N-terminal processing: the methionine aminopeptidase and N alpha-acetyl transferase families

Removal of the initiator methionine and/or acetylation of the alpha-amino group are among the earliest possible chemical modifications that occur during protein synthesis in eukaryotes. These events are catalyzed by methionine aminopeptidase and N alpha-acetyltransferase, respectively. Recent advances in the isolation and characterization of these enzymes indicate that they exist as isoforms that vary in cellular location, function, and evolutionary origins.

The sequence of a 36.7 kb segment on the left arm of chromosome IV from Saccharomyces cerevisiae reveals 20 non-overlapping open reading frames (ORFs) including SIT4, FAD1, NAM1, RNA11, SIR2, NAT1, PRP9, ACT2 and MPS1 and 11 new ORFs

A 36,688 bp fragment from the left arm of chromosome IV of saccharomyces cerevisiae was sequenced. Sequence analysis identified 20 complete non-overlapping open reading frames (ORFs) of at least 100 amino acids. Nine of these correspond to previously identified and sequenced genes: SIT4/PH1, FAD1, NAM1/MTF2, RNA11, SIR2/MAR1, NAT1/AAA1, PRP9, ACT2 and MPS1/RPK1. Three ORFs show homology to previously sequenced genes. One ORF exhibits a hypothetical yabO/yceC/YfiI family signature and one has the ATP-dependent helicase signature of the DEAD and DEAH box families. Six ORFs show no appreciable homology to any proteins in the database. One of these is identical to yeast expressed sequence tags and therefore corresponds to and expressed gene. In addition, two partial ORFs and 11 ORFs that are totally internal and are not likely to be functional were detected.

Yeast MAK3 N-acetyltransferase recognizes the N-terminal four amino acids of the major coat protein (gag) of the L-A double-stranded RNA virus

The MAK3 gene of Saccharomyces cerevisiae encodes an N-acetyltransferase whose acetylation of the N terminus of the L-A double-stranded RNA virus major coat protein (gag) is necessary for viral assembly. We show that the first 4 amino acids of the L-A gag protein sequence, MLRF, are a portable signal for N-terminal acetylation by MAK3. Amino acids 2, 3, and 4 are each important for acetylation by the MAK3 enzyme. In yeast cells, only three mitochondrial proteins are known to have the MAK3 acetylation signal, suggesting an explanation for the slow growth of mak3 mutants on nonfermentable carbon sources.

N alpha acetylation is required for normal growth and mating of Saccharomyces cerevisiae

Acetylation is the most frequently occurring chemical modification of the alpha-NH2 group of eucaryotic proteins and is catalyzed by N alpha-acetyltransferase. The yeast enzyme is encoded by the AAA1 (amino-terminal alpha-amino acetyltransferase) gene. A null mutation (aaa1-1) created by gene replacement, while not lethal, slows cell growth and results in heterogeneous colony morphology. In comparison with wild-type cells, aaa1-1/aaa1-1 diploids cannot enter stationary phase, are sporulation defective, and are sensitive to heat shock. In addition, the aaa1-1 mutation specifically reduces mating functions of MATa cells. These results indicate that N alpha acetylation plays a crucial role in yeast cell growth and mating.

N alpha-acetyltransferase deficiency alters protein synthesis in Saccharomyces cerevisiae

Acetylation is the most frequently occurring chemical modification of the alpha-NH2 group of eukaryotic proteins and is catalyzed by a N alpha-acetyltransferase. Two-dimensional gel electrophoresis was used to compare the soluble proteins synthesized in wild type and a mutant (aaa1) yeast cells lacking N alpha-acetyltransferase. Among 855 soluble proteins identified in wild type and mutant, approximately 20% of the proteins in the mutant either disappeared or were shifted to higher pI without a change of molecular mass, and 27 proteins were observed only in the mutant. In addition, the synthesis of another 12% of the proteins in the mutant was either diminished or enhanced, suggesting that the acetylation of certain regulatory proteins may affect their expression. This is the first demonstration of the broad-based functional role of N alpha-acetylation in eukaryotic protein synthesis.

Purification and characterization of an acetyl-CoA hydrolase from Saccharomyces cerevisiae

Acetyl-CoA hydrolase, which hydrolyzes acetyl-CoA to acetate and CoASH, was isolated from Saccharomyces cerevisiae and demonstrated by protein sequence analysis to be NH2-terminally blocked. The enzyme was purified 1080-fold to apparent homogeneity by successive purification steps using DEAE-Sepharose, gel filtration and hydroxylapatite. The molecular mass of the native yeast acetyl-CoA hydrolase was estimated to be 64 +/- 5 kDa by gel-filtration chromatography. SDS/PAGE analysis revealed that the denatured molecular mass was 65 +/- 2 kDa and together with that for the native enzyme indicates that yeast acetyl-CoA hydrolase was monomeric. The enzyme had a pH optimum near 8.0 and its pI was approximately 5.8. Several acyl-CoA derivatives of varying chain length were tested as substrates for yeast acetyl-CoA hydrolase. Although acetyl-CoA hydrolase was relatively specific for acetyl-CoA, longer acyl-chain CoAs were also hydrolyzed and were capable of functioning as inhibitors during the hydrolysis of acetyl-CoA. Among a series of divalent cations, Zn2+ was demonstrated to be the most potent inhibitor. The enzyme was inactivated by chemical modification with diethyl pyrocarbonate, a histidine-modifying reagent.