Cic1, an adaptor protein specifically linking the 26S proteasome to its substrate, the SCF component Cdc4.

In eukaryotes, the ubiquitin-proteasome system plays a major role in selective protein breakdown for cellular regulation. Here we report the discovery of a new essential component of this degradation machinery. We found the Saccharomyces cerevisiae protein Cic1 attached to 26S proteasomes playing a crucial role in substrate specificity for proteasomal destruction. Whereas degradation of short-lived test proteins is not affected, cic1 mutants stabilize the F-box proteins Cdc4 and Grr1, substrate recognition subunits of the SCF complex. Cic1 interacts in vitro and in vivo with Cdc4, suggesting a function as a new kind of substrate recruiting factor or adaptor associated with the proteasome.

Steady-state free Ca(2+) in the yeast endoplasmic reticulum reaches only 10 microM and is mainly controlled by the secretory pathway pump pmr1.

Over recent decades, diverse intracellular organelles have been recognized as key determinants of Ca(2+) signaling in eukaryotes. In yeast however, information on intra-organellar Ca(2+) concentrations is scarce, despite the demonstrated importance of Ca(2+) signals for this microorganism. Here, we directly monitored free Ca(2+) in the lumen of the endoplasmic reticulum (ER) of yeast cells, using a specifically targeted version of the Ca(2+)-sensitive photoprotein aequorin. Ca(2+) uptake into the yeast ER displayed characteristics distinctly different from the mammalian ER. At steady-state, the free Ca(2+) concentration in the ER lumen was limited to approximately 10 microM, and ER Ca(2+) sequestration was insensitive to thapsigargin, an inhibitor specific for mammalian ER Ca(2+) pumps. In pmr1 null mutants, free Ca(2+) in the ER was reduced by 50%. Our findings identify the secretory pathway pump Pmr1, predominantly localized in the Golgi, as a major component of ER Ca(2+) uptake activity in yeast.

The medial-Golgi ion pump Pmr1 supplies the yeast secretory pathway with Ca2+ and Mn2+ required for glycosylation, sorting, and endoplasmic reticulum-associated protein degradation.

The yeast Ca2+ adenosine triphosphatase Pmr1, located in medial-Golgi, has been implicated in intracellular transport of Ca2+ and Mn2+ ions. We show here that addition of Mn2+ greatly alleviates defects of pmr1 mutants in N-linked and O-linked protein glycosylation. In contrast, accurate sorting of carboxypeptidase Y (CpY) to the vacuole requires a sufficient supply of intralumenal Ca2+. Most remarkably, pmr1 mutants are also unable to degrade CpY*, a misfolded soluble endoplasmic reticulum protein, and display phenotypes similar to mutants defective in the stress response to malfolded endoplasmic reticulum proteins. Growth inhibition of pmr1 mutants on Ca2+-deficient media is overcome by expression of other Ca2+ pumps, including a SERCA-type Ca2+ adenosine triphosphatase from rabbit, or by Vps10, a sorting receptor guiding non-native luminal proteins to the vacuole. Our analysis corroborates the dual function of Pmr1 in Ca2+ and Mn2+ transport and establishes a novel role of this secretory pathway pump in endoplasmic reticulum-associated processes.

The PMR2 gene cluster encodes functionally distinct isoforms of a putative Na+ pump in the yeast plasma membrane.

We report a structural and functional analysis of the PMR2 gene cluster in yeast. We found that several strains of Saccharomyces cerevisiae contain multiple PMR2 genes repeated in tandem, whereas most phylogenetically related yeasts appear to possess only a single PMR2 gene. This unusual tandem array of nearly identical genes encodes putative ion pumps involved in Na+ tolerance. Pmr2a and Pmr2b, the proteins encoded by the first two repeats, differ by only 13 amino acid exchanges. Both proteins share localization to the plasma membrane, but represent distinct isoforms of a putative Na+ pump. When expressed under identical conditions in vivo, Pmr2a and Pmr2b cause different tolerances to Na+ and Li+. Finally, we show that the Na+ tolerance mediated through these pumps is regulated by calmodulin via a calcineurin-independent mechanism which activates the Pmr2 ion pumps post-transcriptionally.

Synthesis of 5-aminopentyl 4,6-O-[(R)-1-carboxyethylidene]-beta-D-galactopyranoside and its use as a ligand for the affinity chromatography of human serum amyloid P . protein.

A series of 2,3-di-O-benzoyl-D-galactopyranosides, alpha-allyl (5), alpha-benzyl (6), beta-ethyl-1-thio (7), beta-phenyl-1-thio (8), and alpha-methyl (9),were prepared from the corresponding 4,6-O-benzylidene derivatives and were acetalated in acetonitrile with methyl pyruvate, to give diastereoselectively the 2,3-di-O-benzoyl-4,6-O-[(R)-1-methoxycarbonylethylidene]-D- galactopyranosides 10-16. The latter were converted into the 2,3-di-O-benzoyl-4,6-O-[(R)-1-methoxycarbonylethylidene]-D-galacto pyranosyl alpha- and beta-trichloroacetimidates 19 and 20, alpha- and beta-fluorides 21 and 22, the alpha-bromide 23, and the alpha-chloride 24, respectively. These donors, including the phenyl 1-thiogalactoside 14, reacted with 5-[(benzyl-oxycarbonyl)amino]pentanol to give the corresponding protected beta-D-galactoside 27, deblocking of which afforded the title compound 1. Binding of 1 to epoxypropyl-modified acrylamide beads gave an affinity adsorbent that was used to isolate serum amyloid P protein from human serum.