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Molecular and Cellular Biology, April 2000, p. 2367-2377, Vol. 20, No. 7
Department of Biochemistry & Molecular
Biology, University of Chicago, Chicago, Illinois 60637
Received 14 October 1999/Returned for modification 11 November
1999/Accepted 3 January 2000
Yeast Smt3 and its vertebrate homolog SUMO-1 are ubiquitin-like
proteins (Ubls) that are reversibly ligated to other proteins. Like
SMT3, SMT4 was first isolated as a
high-copy-number suppressor of a defective centromere-binding
protein. We show here that SMT4 encodes an
Smt3-deconjugating enzyme, Ulp2. In cells lacking Ulp2, specific
Smt3-protein conjugates accumulate, and the conjugate pattern is
distinct from that observed in a ulp1ts strain,
which is defective for a distantly related Smt3-specific protease,
Ulp1. The ulp2
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Copyright © 2000, American Society for Microbiology. All rights reserved.
The Yeast ULP2 (SMT4) Gene
Encodes a Novel Protease Specific for the Ubiquitin-Like Smt3
Protein
mutant exhibits a pleiotropic
phenotype that includes temperature-sensitive growth, abnormal cell
morphology, decreased plasmid and chromosome stability, and a severe
sporulation defect. The mutant is also hypersensitive to
DNA-damaging agents, hydroxyurea, and benomyl. Although cell cycle
checkpoint arrest in response to DNA damage, replication
inhibition, or spindle defects occurs with normal kinetics, recovery
from arrest is impaired. Surprisingly, either introduction of a
ulp1ts mutation or overproduction of
catalytically inactive Ulp1 can substantially overcome the
ulp2
defects. Inactivation of Ulp2 also suppresses
several ulp1ts defects, and the double
mutant accumulates far fewer Smt3-protein conjugates than either single
mutant. Our data suggest the existence of a feedback mechanism that
limits Smt3-protein ligation when Smt3 deconjugation by both Ulp1 and
Ulp2 is compromised, allowing a partial recovery of cell function.
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, University of Chicago, 920 East
58th Street, Chicago, IL 60637. Phone: (773) 702-2117. Fax: (773)
702-0439. E-mail: hoc1{at}midway.uchicago.edu.
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