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Plasticity in eucaryotic 20S proteasome ring assembly revealed by a subunit deletion in yeast
Author(s) -
Velichutina Irina,
Connerly Pamela L,
Arendt Cassandra S,
Li Xia,
Hochstrasser Mark
Publication year - 2004
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/sj.emboj.7600059
Subject(s) - biology , protein subunit , proteasome , yeast , ring (chemistry) , saccharomyces cerevisiae , microbiology and biotechnology , plasticity , genetics , gene , chemistry , organic chemistry , physics , thermodynamics
The 20S proteasome is made up of four stacked heptameric rings, which in eucaryotes assemble from 14 different but related subunits. The rules governing subunit assembly and placement are not understood. We show that a different kind of proteasome forms in yeast when the Pre9/α3 subunit is deleted. Purified pre9Δ proteasomes show a two‐fold enrichment for the Pre6/α4 subunit, consistent with the presence of an extra copy of Pre6 in each outer ring. Based on disulfide engineering and structure‐guided suppressor analyses, Pre6 takes the position normally occupied by Pre9, a substitution that depends on a network of intersubunit salt bridges. When Arabidopsis PAD1/α4 is expressed in yeast, it complements not only pre6 Δ but also pre6 Δ pre9 Δ mutants; therefore, the plant α4 subunit also can occupy multiple positions in a functional yeast proteasome. Importantly, biogenesis of proteasomes is delayed at an early stage in pre9 Δ cells, suggesting an advantage for Pre9 over Pre6 incorporation at the α3 position that facilitates correct assembly.