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A proteasome cap subunit required for spindle pole body duplication in yeast.

McDonald HB, Byers B - J. Cell Biol. (1997)

Bottom Line: Biol.EM reveals that each arrested pcs1 cell has failed to duplicate its spindle pole body (SPB), which becomes enlarged as in other monopolar mutants.We hypothesize that Pcs1p plays a role in the degradation of certain potentially nuclear component(s) in a manner that specifically is required for SPB duplication.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, University of Washington, Seattle 98195, USA.

ABSTRACT
Proteasome-mediated protein degradation is a key regulatory mechanism in a diversity of complex processes, including the control of cell cycle progression. The selection of substrates for degradation clearly depends on the specificity of ubiquitination mechanisms, but further regulation may occur within the proteasomal 19S cap complexes, which attach to the ends of the 20S proteolytic core and are thought to control entry of substrates into the core. We have characterized a gene from Saccharomyces cerevisiae that displays extensive sequence similarity to members of a family of ATPases that are components of the 19S complex, including human subunit p42 and S. cerevisiae SUG1/CIM3 and CIM5 products. This gene, termed PCS1 (for proteasomal cap subunit), is identical to the recently described SUG2 gene (Russell, S.J., U.G. Sathyanarayana, and S.A. Johnston. 1996. J. Biol. Chem. 271:32810-32817). We have shown that PCS1 function is essential for viability. A temperature-sensitive pcs1 strain arrests principally in the second cycle after transfer to the restrictive temperature, blocking as large-budded cells with a G2 content of unsegregated DNA. EM reveals that each arrested pcs1 cell has failed to duplicate its spindle pole body (SPB), which becomes enlarged as in other monopolar mutants. Additionally, we have shown localization of a functional Pcs1-green fluorescent protein fusion to the nucleus throughout the cell cycle. We hypothesize that Pcs1p plays a role in the degradation of certain potentially nuclear component(s) in a manner that specifically is required for SPB duplication.

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Schematic representation of a 26S proteasome. The 20S  proteolytic barrel structure is indicated in pale grey and the 19S  cap structures at either end are in dark grey. The caps are believed to recognize ubiquitinated proteins, unfold them, and feed  them into the proteolytic core in an ATP-dependent manner, resulting in the release of peptides and free ubiquitin.
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Figure 1: Schematic representation of a 26S proteasome. The 20S proteolytic barrel structure is indicated in pale grey and the 19S cap structures at either end are in dark grey. The caps are believed to recognize ubiquitinated proteins, unfold them, and feed them into the proteolytic core in an ATP-dependent manner, resulting in the release of peptides and free ubiquitin.

Mentions: Poly-ubiquitinated proteins are degraded by proteasomes (33, 41, 75; for exceptions see 40), which are distributed throughout both the cytoplasm and the nucleus of eukaryotic cells (76). Each 26S proteasome is assembled in an ATP-dependent manner (28, 63) from a cylindrical 20S core and two 19S complexes that cap the ends of the cylinder (75) (Fig. 1). The x-ray crystal structure of the 20S complex from the archaebacterium Thermoplasma acidophilum was recently determined (60). This complex, which EM reveals to be structurally similar to the eukaryotic 20S particle (78), was shown to consist of four stacked ring structures. In T. acidophilum, each of the two outer rings consists of seven identical α subunits, while each of the inner rings consists of seven identical β subunits. Each β subunit has a proteolytic site facing the interior of the 20S cylinder, effectively sequestering its activity away from proteins that lie outside the cylinder. In eukaryotes, the rings are formed of nonidentical but related subunits. Seven related α subunit– and seven related β subunit–encoding genes have been identified in S. cerevisiae (41), suggesting that each ring might contain seven different subunits. It is likely that all 20S proteasomal cores in S. cerevisiae are identical, each one containing all 14 distinct α and β subunits (11).


A proteasome cap subunit required for spindle pole body duplication in yeast.

McDonald HB, Byers B - J. Cell Biol. (1997)

Schematic representation of a 26S proteasome. The 20S  proteolytic barrel structure is indicated in pale grey and the 19S  cap structures at either end are in dark grey. The caps are believed to recognize ubiquitinated proteins, unfold them, and feed  them into the proteolytic core in an ATP-dependent manner, resulting in the release of peptides and free ubiquitin.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139890&req=5

Figure 1: Schematic representation of a 26S proteasome. The 20S proteolytic barrel structure is indicated in pale grey and the 19S cap structures at either end are in dark grey. The caps are believed to recognize ubiquitinated proteins, unfold them, and feed them into the proteolytic core in an ATP-dependent manner, resulting in the release of peptides and free ubiquitin.
Mentions: Poly-ubiquitinated proteins are degraded by proteasomes (33, 41, 75; for exceptions see 40), which are distributed throughout both the cytoplasm and the nucleus of eukaryotic cells (76). Each 26S proteasome is assembled in an ATP-dependent manner (28, 63) from a cylindrical 20S core and two 19S complexes that cap the ends of the cylinder (75) (Fig. 1). The x-ray crystal structure of the 20S complex from the archaebacterium Thermoplasma acidophilum was recently determined (60). This complex, which EM reveals to be structurally similar to the eukaryotic 20S particle (78), was shown to consist of four stacked ring structures. In T. acidophilum, each of the two outer rings consists of seven identical α subunits, while each of the inner rings consists of seven identical β subunits. Each β subunit has a proteolytic site facing the interior of the 20S cylinder, effectively sequestering its activity away from proteins that lie outside the cylinder. In eukaryotes, the rings are formed of nonidentical but related subunits. Seven related α subunit– and seven related β subunit–encoding genes have been identified in S. cerevisiae (41), suggesting that each ring might contain seven different subunits. It is likely that all 20S proteasomal cores in S. cerevisiae are identical, each one containing all 14 distinct α and β subunits (11).

Bottom Line: Biol.EM reveals that each arrested pcs1 cell has failed to duplicate its spindle pole body (SPB), which becomes enlarged as in other monopolar mutants.We hypothesize that Pcs1p plays a role in the degradation of certain potentially nuclear component(s) in a manner that specifically is required for SPB duplication.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, University of Washington, Seattle 98195, USA.

ABSTRACT
Proteasome-mediated protein degradation is a key regulatory mechanism in a diversity of complex processes, including the control of cell cycle progression. The selection of substrates for degradation clearly depends on the specificity of ubiquitination mechanisms, but further regulation may occur within the proteasomal 19S cap complexes, which attach to the ends of the 20S proteolytic core and are thought to control entry of substrates into the core. We have characterized a gene from Saccharomyces cerevisiae that displays extensive sequence similarity to members of a family of ATPases that are components of the 19S complex, including human subunit p42 and S. cerevisiae SUG1/CIM3 and CIM5 products. This gene, termed PCS1 (for proteasomal cap subunit), is identical to the recently described SUG2 gene (Russell, S.J., U.G. Sathyanarayana, and S.A. Johnston. 1996. J. Biol. Chem. 271:32810-32817). We have shown that PCS1 function is essential for viability. A temperature-sensitive pcs1 strain arrests principally in the second cycle after transfer to the restrictive temperature, blocking as large-budded cells with a G2 content of unsegregated DNA. EM reveals that each arrested pcs1 cell has failed to duplicate its spindle pole body (SPB), which becomes enlarged as in other monopolar mutants. Additionally, we have shown localization of a functional Pcs1-green fluorescent protein fusion to the nucleus throughout the cell cycle. We hypothesize that Pcs1p plays a role in the degradation of certain potentially nuclear component(s) in a manner that specifically is required for SPB duplication.

Show MeSH
Related in: MedlinePlus