title: Thermolability of ubiquitin-activating enzyme from the mammalian cell cycle mutant ts85.
abstract: Ubiquitin, a 76 residue protein, occurs in eucaryotic cells either free or covalently joined to a variety of protein species. Previous work suggested that ubiquitin may function as a signal for attack by proteinases specific for ubiquitin-protein conjugates. We show that the mouse cell line ts85 , a previously isolated cell cycle mutant, is temperature-sensitive in ubiquitin-protein conjugation, and that this effect is due to the specific thermolability of the ts85 ubiquitin-activating enzyme (E1). From E1 thermoinactivation kinetics in mixed (wild-type plus ts85 ) extracts, and from copurification of the determinant of E1 thermolability with E1 in ubiquitin-affinity chromatography, we conclude that the determinant of E1 thermolability is contained within the E1 polypeptide. ts85 cells fail to degrade otherwise short-lived intracellular proteins at the nonpermissive temperature (accompanying paper), demonstrating that degradation of the bulk of short-lived proteins in this higher eucaryotic cell proceeds through a ubiquitin-dependent pathway. We discuss possible roles of ubiquitin-dependent pathways in DNA transactions, the cell cycle, and the heat shock response.
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002846:Chromatography, Affinity; D002868:Chromosomal Proteins, Non-Histone / Q000302:isolation & purification / Q000378:metabolism; D005260:Female; D006657:Histones / Q000378:metabolism; D006358:Hot Temperature; D008025:Ligases / Q000378:metabolism*; D008325:Mammary Neoplasms, Experimental / Q000503:physiopathology; D051379:Mice; D008970:Molecular Weight; D009154:Mutation; D009698:Nucleoproteins / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D006657:Histones; D009698:Nucleoproteins; D014452:Ubiquitins; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D044764:Ubiquitin-Activating Enzymes