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  • 1995-1999  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Functional analysis of the proteasome regulatory particle (1999)
    Springer
    Molecular biology reports 26 (1999), S. 21-28 
    Details
    ISSN: 1573-4978
    Keywords: ATPase ; proteasome ; S. cerevisiae ; ubiquitin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have developed S. cerevisiae as a model system for mechanistic studies of the 26S proteasome. The subunits of the yeast 19S complex, or regulatory particle (RP), have been defined, and are closely related to those of mammalian proteasomes. The multiubiquitin chain binding subunit (S5a/Mcb1/Rpn10) was found, surprisingly, to be nonessential for the degradation of a variety of ubiquitin-protein conjugates in vivo. Biochemical studies of proteasomes from Δrpn10 mutants revealed the existence of two structural subassemblies within the RP, the lid and the base. The lid and the base are both composed of 8 subunits. By electron microscopy, the base and the lid correspond to the proximal and distal masses of the RP, respectively. The base is sufficient to activate the 20S core particle for degradation of peptides, but the lid is required for ubiquitin-dependent degradation. The lid subunits share sequence motifs with components of the COP9/signalosome complex, suggesting that these functionally diverse particles have a common evolutionary ancestry. Analysis of equivalent point mutations in the six ATPases of the base indicate that they have well-differentiated functions. In particular, mutations in one ATPase gene, RPT2, result in an unexpected defect in peptide hydrolysis by the core particle. One interpretation of this result is that Rpt2 participates in gating of the channel through which substrates enter the core particle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006928316738
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  • 2
    Electronic Resource
    Electronic Resource
    ATPase and ubiquitin-binding proteins of the yeast proteasome (1997)
    Springer
    Molecular biology reports 24 (1997), S. 17-26 
    Details
    ISSN: 1573-4978
    Keywords: ATPase ; S. cerevisiae ; protease ; proteasome ; ubiquitin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The 26S proteasome is a 2-Megadalton proteolytic complex with over 30 distinct subunits. The 19S particle, a subcomplex of the 26S proteasome, is thought to confer ATP-dependence and ubiquitin-dependence on the proteolytic core particle of the proteasome. Given the complexity of the 19S particle, genetic approaches are likely to play an important role in its analysis. We have initiated biochemical and genetic studies of the 19S particle in Saccharomyces cerevisiae. Here we describe the localization to the proteasome of several ATPases that were previously proposed to be involved in transcription. Independent studies indicate that the mammalian 26S proteasome contains closely related ATPases. We have also found that the multiubiquitin chain binding protein Mcb1, a homolog of the mammalian S5a protein, is a subunit of the yeast proteasome. However, contrary to expectation, MCB1 is not an essential gene in yeast. The mcb1 mutant grows at a nearly wild-type rate, and the breakdown of most ubiquitin-protein conjugates is unaffected in this strain. One substrate, Ub-Proline-βgal, was found to require MCB1 for its breakdown, but it remains unclear whether Mcb1 serves as a ubiquitin receptor in this process. Our data suggest that the recognition of ubiquitin conjugates by the proteasome is a complex process which must involve proteins other than Mcb1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006844305067
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  • 3
    Electronic Resource
    Electronic Resource
    Structure and functional analyses of the 26S proteasome subunits from plants – Plant 26S proteasome (1999)
    Springer
    Molecular biology reports 26 (1999), S. 137-146 
    Details
    ISSN: 1573-4978
    Keywords: Arabidopsis ; Physcomitrella patens ; proteasome ; proteolysis ; ubiquitin ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract As initial steps to define how the 26S proteasome degrades ubiquitinated proteins in plants, we have characterized many of the subunits that comprise the proteolytic complex from Arabidopsis thaliana. A set of 23 Arabidopsis genes encoding the full complement of core particle (CP) subunits and a collection encoding 12 out of 18 known eukaryotic regulatory particle (RP) subunits, including six AAA-ATPase subunits, were identified. Several of these 26S proteasome genes could complement yeast strains missing the corresponding orthologs. Using this ability of plant subunits to functionally replace yeast counterparts, a parallel structure/function analysis was performed with the RP subunit RPN10/MCB1, a putative receptor for ubiquitin conjugates. RPN10 is not essential for yeast viability but is required for amino acid analog tolerance and degradation of proteins via the ubiquitin-fusion degradation pathway, a subpathway within the ubiquitin system. Surprisingly, we found that the C-terminal motif required for conjugate recognition by RPN10 is not essential for in vivo functions. Instead, a domain near the N-terminus is required. We have begun to exploit the moss Physcomitrella patens as a model to characterize the plant 26S proteasome using reverse genetics. By homologous recombination, we have successfully disrupted the RPN10 gene. Unlike yeast rpn10Δ strains which grow normally, Physcomitrella rpn10Δ strains are developmentally arrested, being unable to initiate gametophorogenesis. Further analysis of these mutants revealed that RPN10 is likely required for a developmental program triggered by plant hormones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006926322501
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  • 4
    Electronic Resource
    Electronic Resource
    Use of alternate splice sites in granule-bound starch synthase mRNA from low-amylose rice varieties (1998)
    Springer
    Plant molecular biology 38 (1998), S. 407-415 
    Details
    ISSN: 1573-5028
    Keywords: rice ; waxy ; splicing ; gene expression ; intron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The rice Waxy gene encodes a granule-bound starch synthase (GBSS) necessary for the synthesis of amylose in endosperm tissue. We have previously shown that a CT microsatellite near the transcriptional start site of the GBSS gene can distinguish 7 alleles that accounted for more than 80% of the variation in apparent amylose content in an extended pedigree of 89 US rice cultivars (Oryza sativa L.). Furthermore, all the cultivars with 18% or less amylose were shown to have the sequence AGTTATA at the putative leader intron 5′ splice site, while all cultivars with a higher proportion of amylose had AGGTATA. Here we demonstrate that this single-base mutation reduces the efficiency of GBSS pre-mRNA processing and results in alternate splicing at three cryptic sites. The predominant 5′ splice site in CT18 low-amylose varieties is 93 bp upstream of the splice site used in intermediate and high amylose varieties and is immediately 5′ to the CT microsatellite that we previously demonstrated to be tightly correlated with amylose content. Use of the leader intron 5′ splice site at either -93 or -1 in conjunction with the predominant 3′ splice site results in formation of a small open reading frame 38 bp upstream of the normal ATG and out of frame with it. This open reading frame is not produced when any of the 5′ leader intron splice sites are used in conjunction with an alternate 3′ splice site five bases further downstream which was observed in all rice varieties tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006021807799
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