Table 2.

Previously reported ubiquitin-independent substrates of proteasome-dependent degradation

Substrate protein	Reference
Ornithine decarboxylase	Rosenberg-Hasson et al. (1989); Coffino (2001)
pRB	Sdek et al. (2005)
pRB family proteinsa	Kalejta and Shenk (2003)
HMG-CoA	Ness and Holland (2005)
Thymidylate synthase	Pena et al. (2005)
α-catenin	Hwang et al. (2005)
P21	Jin et al. (2003); Chen et al. (2004)
RPN4	Ju and Xie (2004)
IκBα	Kretz-Remy and Arrigo (2003)
TCRα	Kretz-Remy and Arrigo (2003)
Calmodulin	Benaroudj et al. (2001)
Troponin C	Benaroudj et al. (2001)
α-synuclein	Tofaris et al. (2001)
SRC-3/AIB1 coactivator	Li et al. (2006)

Abbreviation: SRC, spleen repopulating cells. Table showing the variety of substrates that have been reported in the literature to be degraded by the proteasome in a ubiquitin-independent manner.

^aDegraded by a viral protein.