title: The intrinsically disordered Sem1 protein functions as a molecular tether during proteasome lid biogenesis.
abstract: The intrinsically disordered yeast protein Sem1 (DSS1 in mammals) participates in multiple protein complexes, including the proteasome, but its role(s) within these complexes is uncertain. We report that Sem1 enforces the ordered incorporation of subunits Rpn3 and Rpn7 into the assembling proteasome lid. Sem1 uses conserved acidic segments separated by a flexible linker to grasp Rpn3 and Rpn7. The same segments are used for protein binding in other complexes, but in the proteasome lid they are uniquely deployed for recognizing separate polypeptides. We engineered TEV protease-cleavage sites into Sem1 to show that the tethering function of Sem1 is important for the biogenesis and integrity of the Rpn3-Sem1-Rpn7 ternary complex but becomes dispensable once the ternary complex incorporates into larger lid precursors. Thus, although Sem1 is a stoichiometric component of the mature proteasome, it has a distinct, chaperone-like function specific to early stages of proteasome assembly.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520-8114, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Tomko
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520-8114, USA. Electronic address: mark.hochstrasser@yale.edu.
authors.forename: Mark
authors.initials: M
authors.lastname: Hochstrasser
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D008954:Models, Biological; D008969:Molecular Sequence Data; D046988:Proteasome Endopeptidase Complex / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D016415:Sequence Alignment
chemical_list: C403291:RPN3 protein, S cerevisiae; C519193:Rpn7 protein, S cerevisiae; C117424:SEM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D046988:Proteasome Endopeptidase Complex