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Role Of Sec61alpha In The Regulated Transfer Of The Ribosome-Nascent Chain Complex From The Signal Recognition Particle To The Translocation Channel, Weiqun Song, David Raden, Elisabet Mandon, Reid Gilmore Feb 2012

Role Of Sec61alpha In The Regulated Transfer Of The Ribosome-Nascent Chain Complex From The Signal Recognition Particle To The Translocation Channel, Weiqun Song, David Raden, Elisabet Mandon, Reid Gilmore

Elisabet Mandon

Targeting of ribosome-nascent chain complexes to the translocon in the endoplasmic reticulum is mediated by the concerted action of the signal recognition particle (SRP) and the SRP receptor (SR). Ribosome-stripped microsomes were digested with proteases to sever cytoplasmic domains of SRalpha, SRbeta, TRAM, and the Sec61 complex. We characterized protein translocation intermediates that accumulate when Sec61alpha or SRbeta is inactivated by proteolysis. In the absence of a functional Sec61 complex, dissociation of SRP54 from the signal sequence is blocked. Experiments using SR proteoliposomes confirmed the assembly of a membrane-bound posttargeting intermediate. These results strongly suggest that the Sec61 complex regulates …


A Monomeric Protein In The Golgi Membrane Catalyzes Both N-Deacetylation And N-Sulfation Of Heparan Sulfate, Elisabet Mandon, Ellis Kempner, Masayuki Ishihara, Carlos Hirschberg Feb 2012

A Monomeric Protein In The Golgi Membrane Catalyzes Both N-Deacetylation And N-Sulfation Of Heparan Sulfate, Elisabet Mandon, Ellis Kempner, Masayuki Ishihara, Carlos Hirschberg

Elisabet Mandon

Recent studies have shown that the rat liver heparan sulfate N-deacetylase/N-sulfotransferase is a glycoprotein encoded by a single polypeptide chain of 882 amino acids. Using radiation inactivation analyses, we have now determined that in rat liver Golgi vesicles the target size for the N-deacetylase is 88 +/- 14 kDa, whereas that of the N-sulfotransferase is 92 +/- 8 kDa. These results, together with previous biochemical and molecular cloning approaches, demonstrate that 1) in rat liver Golgi membranes there exists only on population of molecules expressing both activities, 2) the active protein in the Golgi membrane functions as a monomer, and …


A Mutant Yeast Deficient In Golgi Transport Of Uridine Diphosphate N-Acetylglucosamine, Claudia Abeijon, Elisabet Mandon, Phillips Robbins, Carlos Hirschberg Feb 2012

A Mutant Yeast Deficient In Golgi Transport Of Uridine Diphosphate N-Acetylglucosamine, Claudia Abeijon, Elisabet Mandon, Phillips Robbins, Carlos Hirschberg

Elisabet Mandon

Mannan chains of Kluyveromyces lactis mannoproteins are similar to those of Saccharomyces cerevisiae except that they have terminal alpha1-->2-linked N-acetylglucosamine and lack mannose phosphate. In a previous study, Douglas and Ballou (Douglas, R. K., and Ballou, C. E. (1982) Biochemistry 21, 1561-1570) characterized a mutant, mnn2-2, which lacked terminal N-acetylglucosamine in its mannoproteins. The mutant had normal levels of N-acetylglucosaminyltransferase activity, and the partially purified enzyme from wild-type and mutant cells had the same apparent size, heat stability, affinity for substrates, metal requirement, and subcellular location. No qualitative or quantitative differences were found between mutant and wild-type cells in …


An Interaction Between The Srp Receptor And The Translocon Is Critical During Cotranslational Protein Translocation, Ying Jiang, Zhiliang Cheng, Elisabet Mandon, Reid Gilmore Feb 2012

An Interaction Between The Srp Receptor And The Translocon Is Critical During Cotranslational Protein Translocation, Ying Jiang, Zhiliang Cheng, Elisabet Mandon, Reid Gilmore

Elisabet Mandon

The signal recognition particle (SRP)-dependent targeting pathway facilitates rapid, efficient delivery of the ribosome-nascent chain complex (RNC) to the protein translocation channel. We test whether the SRP receptor (SR) locates a vacant protein translocation channel by interacting with the yeast Sec61 and Ssh1 translocons. Surprisingly, the slow growth and cotranslational translocation defects caused by deletion of the transmembrane (TM) span of yeast SRbeta (SRbeta-DeltaTM) are exaggerated when the SSH1 gene is disrupted. Disruption of the SBH2 gene, which encodes the beta subunit of the Ssh1p complex, likewise causes a growth defect when combined with SRbeta-DeltaTM. Cotranslational translocation defects in the …