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20 S proteasomes are assembled via distinct precursor complexes processing of LMP2 and LMP7 proproteins takes place in 13–16 S preproteasome complexes

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Abstract

The non-essential mouse proteasome β-type subunits LMP2 and LMP7 are thought to connect proteasomes to the MHC class I antigen processing pathway. Both subunits are synthesized as proproteins. We have studied the processing of both subunits, correlated with the maturation of 20 S proteasomes in mouse T cells. Our data show that proteasome assembly occurs via 13–16 S precursor complexes which posses a protein pattern distinct from that of 20 S proteasomes. Both LMP2 and LMP7 proproteins are processed within these preproteasome complexes and only their processed forms become part of active 20 S proteasomes. Our data show that the maturation and assembly of 20 S proteasomes via precursor particles is a translation-dependent gradual process, that processing of subunit proproteins takes place in these 13–16 S complexes and that subunit processing and proteasome formation occur together.

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    Present address of corresponding author: Peter-M. Kloetzel. Institut für Biochemie-Charité, Humboldt Universität zu Berlin, Hessiche Straß 3–4, 10115 Berlin, FRG.

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