期刊
JOURNAL OF MOLECULAR BIOLOGY
卷 301, 期 1, 页码 1-9出版社
ACADEMIC PRESS LTD
DOI: 10.1006/jmbi.2000.3959
关键词
20 S proteasome; ATP-dependent proteolysis; proteasome maturation factor; LMP7; 16 S precursor
Biogenesis of mammalian 20 S proteasomes occurs via precursor complexes containing a and unprocessed beta subunits. A human homologue of the yeast proteasome maturation factor Ump1 was identified in 2D gels of 16 S precursor preparations and designated as POMP (proteasome maturation protein). We show that POMP is detected only in precursor fractions and not in fractions containing mature 20 S proteasome. Northern blot experiments revealed that expression of POMP is induced after treatment with interferon gamma. To analyse the role of the beta 5 propeptide for proper maturation and incorporation of the beta 5 subunit into the complex, human T2 cells, which highly express derivatives of the beta 5i subunit (LMP7), were studied. In contrast to yeast, the presence of the beta 5 propeptide is not essential for incorporation of LMP7 into the proteasome complex. Mutated LMP7 subunits either carrying the prosequence of beta 2i (LMP2) or containing a mutation in the active threonine site are incorporated like wild-type LMP7, while a LMP7 derivative lacking the prosequence completely is incorporated to a lesser extent. Although the absence of the prosequence does not affect incorporation of LMP7, its deletion leads to delayed proteasome maturation and thereby to an accumulation of precursor complexes. As a result of the precursor accumulation, an increased amount of the POMP protein can be detected in these cells. (C) 2000 Academic Press.
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