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A novel mammalian Smt3âspecific isopeptidase 1 (SMT3IP1) localized in the nucleolus at interphase
- Nishida, Tamotsu, Tanaka, Hirofumi, Yasuda, Hideyo
- European journal of biochemistry 2000 v.267 no.21 pp. 6423-6427
- Saccharomyces cerevisiae, active sites, cell nucleolus, cysteine, enzymes, histidine, humans, interphase, two hybrid system techniques, ubiquitin, yeasts
- A novel Smt3âspecific isopeptidase, SMT3IP1, was cloned using a yeast twoâhybrid screen with Smt3b as bait. The clone, named SMT3IP1 (Smt3âspecific isopeptidase 1), which bound to Smt3b but not SUMOâ1 in the twoâhybrid system, was distantly related to budding yeast Saccharomyces cerevisiae Ulp1, human SENP1 or human SUSP1. The catalytic domains in the Câterminal region were very similar, but the Nâterminal region was quite different to other enzymes. The cysteine, histidine and asparatic acid residues in the catalytic domains were conserved. SMT3IP1 expressed by the baculovirusâexpression system had the ability to cleave SUMOâ1 or Smt3b from SUMOâ1/RanGAP1 or Smt3b/RanGAP1 conjugates, respectively, and the activity was a little stronger towards the Smt3b conjugate than towards the SUMOâ1 conjugate. Furthermore, the enzyme bound more strongly to Smt3a and Smt3b than to SUMOâ1 in vitro. The enzyme did not cleave Nedd8 from Nedd8/cullinâ1. Nor did it cleave ubiquitin from ubiquitinated p53. SMT3IP1 was localized almost exclusively at the nucleolus during interphase. The Nâterminal sequence was responsible for the nucleolar localization of this enzyme. Whether SMT3IP1 functions in the nucleolus or just stays there before it functions in the nucleus, as shown in the case of CDC14 phosphatase, remains to be elucidated.