title: The interaction of the chaperonin tailless complex polypeptide 1 (TCP1) ring complex (TRiC) with ribosome-bound nascent chains examined using photo-cross-linking.
abstract: The eukaryotic chaperonin tailless complex polypeptide 1 (TCP1) ring complex (TRiC) (also called chaperonin containing TCP1 [CCT]) is a hetero-oligomeric complex that facilitates the proper folding of many cellular proteins. To better understand the manner in which TRiC interacts with newly translated polypeptides, we examined its association with nascent chains using a photo-cross-linking approach. To this end, a series of ribosome-bound nascent chains of defined lengths was prepared using truncated mRNAs. Photoactivatable probes were incorporated into these (35)S- labeled nascent chains during translation. Upon photolysis, TRiC was cross-linked to ribosome-bound polypeptides exposing at least 50-90 amino acids outside the ribosomal exit channel, indicating that the chaperonin associates with much shorter nascent chains than indicated by previous studies. Cross-links were observed for nascent chains of the cytosolic proteins actin, luciferase, and enolase, but not to ribosome-bound preprolactin. The pattern of cross-links became more complex as the nascent chain increased in length. These results suggest a chain length-dependent increase in the number of TRiC subunits involved in the interaction that is consistent with the idea that the substrate participates in subunit-specific contacts with the chaperonin. Both ribosome isolation by centrifugation through sucrose cushions and immunoprecipitation with anti-puromycin antibodies demonstrated that the photoadducts form on ribosome-bound polypeptides. Our results indicate that TRiC/CCT associates with the translating polypeptide shortly after it emerges from the ribosome and suggest a close association between the chaperonin and the translational apparatus.
authors.affiliation: Department of Medical Biochemistry and Genetics, Texas A&M University, College Station, Texas 77843-1114, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: McCallum
authors.forename: H
authors.initials: H
authors.lastname: Do
authors.forename: A E
authors.initials: AE
authors.lastname: Johnson
authors.forename: J
authors.initials: J
authors.lastname: Frydman
mesh_terms: D000199:Actins / Q000737:chemistry / Q000235:genetics; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000378:metabolism*; D003432:Cross-Linking Reagents; D047908:Intracellular Signaling Peptides and Proteins; D008156:Luciferases / Q000737:chemistry / Q000235:genetics; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins / Q000378:metabolism; D010751:Phosphopyruvate Hydratase / Q000737:chemistry / Q000235:genetics; D010782:Photolysis; D011233:Precipitin Tests; D014176:Protein Biosynthesis; D017510:Protein Folding; D011691:Puromycin / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D012357:RNA, Transfer, Lys / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry; D012156:Reticulocytes / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D056427:t-Complex Genome Region
chemical_list: D000199:Actins; D003432:Cross-Linking Reagents; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D012357:RNA, Transfer, Lys; D016601:RNA-Binding Proteins; C533304:TCP1 protein, human; D011691:Puromycin; D000255:Adenosine Triphosphate; D008156:Luciferases; C116196:PPP1R11 protein, human; D044767:Ubiquitin-Protein Ligases; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins; D010751:Phosphopyruvate Hydratase