The ubiquitin-like protein Smt3p is activated for conjugation to other proteins by an Aos1p/Uba2p heterodimer.
SMT3 is an essential Saccharomyces cerevisiae gene encoding a 11.5 kDa protein similar to the mammalian ubiquitin-like protein SUMO-1. We have found that Smt3p, like SUMO-1 and ubiquitin, can be attached to other proteins post-translationally and have characterized the processes leading to the activation of the Smt3p C-terminus for conjugation. First, the SMT3 translation product is cleaved endoproteolytically to expose Gly98, the mature C-terminus. The presence of Gly98 is critical for Smt3p's abilities to be conjugated to protein substrates and to complement the lethality of a smt3Delta strain. Smt3p undergoes ATP-dependent activation by a novel heterodimeric enzyme consisting of Uba2p, a previously identified 71 kDa protein similar to the C-terminus of ubiquitin-activating enzymes (E1s), and Aos1p (activation of Smt3p), a 40 kDa protein similar to the N-terminus of E1s. Experiments with conditional uba2 mutants showed that Uba2p is required for Smt3p conjugation in vivo. Furthermore, UBA2 and AOS1 are both essential genes, providing additional evidence that they act in a distinct pathway whose role in cell viability is to conjugate Smt3p to other proteins.
Johnson
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Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, NY 10021, USA. johnsoe@rockvax.rockefeller.edu
Schwienhorst
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Dohmen
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Blobel
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D000483:Alleles; D000595:Amino Acid Sequence; D001665:Binding Sites; D002470:Cell Survival; D019281:Dimerization; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism; D005816:Genetic Complementation Test; D005998:Glycine; D006801:Humans; D008025:Ligases / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011960:Receptors, Estrogen / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D025841:Small Ubiquitin-Related Modifier Proteins; D044764:Ubiquitin-Activating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000737:chemistry
D005656:Fungal Proteins; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C099362:SMT3 protein, S cerevisiae; C117909:SUMO2 protein, human; D029701:Saccharomyces cerevisiae Proteins; D025841:Small Ubiquitin-Related Modifier Proteins; C470301:UBA2 protein, human; D014452:Ubiquitins; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D044764:Ubiquitin-Activating Enzymes; D005998:Glycine