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We report that subunits of human nuclear proteasomes carry a previously unrecognised, constitutive posttranslational modification. Subunits with this modification are not visualised by SDS-PAGE, which is used in almost all denaturing protein gel electrophoresis. In contrast, CTAB-PAGE readily visualises such modified subunits. Thus, under most experimental conditions, with identical samples, SDS-PAGE yielded gel electrophoresis patterns for subunits of nuclear proteasomes which were misleading and strikingly different from those obtained with CTAB-PAGE. Initial analysis indicates a novel modification of a high negative charge with some similarity to polyADP-ribose, possibly explaining compatibility with (positively-charged) CTAB-PAGE but not (negatively-charged) SDS-PAGE and providing a mechanism for how nuclear proteasomes may interact with chromatin, DNA and other nuclear components.

Original publication

DOI

10.1016/j.bbapap.2014.08.013

Type

Journal article

Journal

Biochim Biophys Acta

Publication Date

12/2014

Volume

1844

Pages

2222 - 2228

Keywords

ADP-ribose, Apoptosis, CTAB-PAGE, Nuclear biology, Proteasome, Ubiquitin