Protein synthesis elongation factor EF-1 alpha is essential for ubiquitin-dependent degradation of certain N alpha-acetylated proteins and may be substituted for by the bacterial elongation factor EF-Tu.
Targeting of different cellular proteins for conjugation and subsequent degradation via the ubiquitin pathway involves diverse recognition signals and distinct enzymatic factors. A few proteins are recognized via their N-terminal amino acid residue and conjugated by a ubiquitin-protein ligase that recognizes this residue. Most substrates, including the N alpha-acetylated proteins that constitute the vast majority of cellular proteins, are targeted by different signals and are recognized by yet unknown ligases. We have previously shown that degradation of N-terminally blocked proteins requires a specific factor, designated FH, and that the factor acts along with the 26S protease complex to degrade ubiquitin-conjugated proteins. Here, we demonstrate that FH is the protein synthesis elongation factor EF-1 alpha. (a) Partial sequence analysis reveals 100% identity to EF-1 alpha. (b) Like EF-1 alpha, FH binds to immobilized GTP (or GDP) and can be purified in one step using the corresponding nucleotide for elution. (c) Guanine nucleotides that bind to EF-1 alpha protect the ubiquitin system-related activity of FH from heat inactivation, and nucleotides that do not bind do not exert this effect. (d) EF-Tu, the homologous bacterial elongation factor, can substitute for FH/EF-1 alpha in the proteolytic system. This last finding is of particular interest since the ubiquitin system has not been identified in prokaryotes. The activities of both EF-1 alpha and EF-Tu are strongly and specifically inhibited by ubiquitin-aldehyde, a specific inhibitor of ubiquitin isopeptidases. It appears, therefore, that EF-1 alpha may be involved in releasing ubiquitin from multiubiquitin chains, thus rendering the conjugates susceptible to the action of the 26S protease complex.
Gonen
H
H
Department of Biochemistry, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
Smith
C E
CE
Siegel
N R
NR
Kahana
C
C
Merrick
W C
WC
Chakraburtty
K
K
Schwartz
A L
AL
Ciechanover
A
A
D000107:Acetylation; D000595:Amino Acid Sequence; D000818:Animals; D004926:Escherichia coli / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D008969:Molecular Sequence Data; D020648:Peptide Elongation Factor 1; D010444:Peptide Elongation Factor Tu / Q000378:metabolism; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D017421:Sequence Analysis; D013045:Species Specificity; D014452:Ubiquitins / Q000378:metabolism*
D006657:Histones; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors; D011506:Proteins; D014452:Ubiquitins; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D019204:GTP-Binding Proteins; D010444:Peptide Elongation Factor Tu