Polyubiquitin receptors execute the targeting of polyubiquitylated proteins
to the 26S proteasome. In vitro studies indicate that disturbance of the
physiological balance among different receptor proteins impairs the prote-asomal degradation of polyubiquitylated proteins.
The recognition of ubiquitylated substrates is an essential element of ubiqu-itin⁄26S proteasome-mediated proteolysis (UPP), which is mediated directly
by the proteasome subunit RPN10 and⁄or RPN13, or indirectly by ubiquitin
receptors containing ubiquitin-like and ubiquitin-associated domains. By
pull-down and mutagenesis assays, we detected cross-species divergence of
the major recognition pathways.
The Rpn10 subunit of the 26S proteasome can bind to polyubiqui-tinoylated and⁄or ubiquitin-like proteins via ubiquitin-interacting motifs
(UIMs). Vertebrate Rpn10 consists of five distinct spliced isoforms, but the
specific functions of these variants remain largely unknown.
We performed a functional genetic screen to find novel antiapoptotic genes
that are under the regulation of the oncoprotein c-Src. Several clones were
identified, including subunit S5a of the 26Sproteasome. We found that
S5a rescued Saos-2 cells from apoptosis induced by Src inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1).
Parkinson’s disease is characterized by the loss of dopaminergic neurons
in the nigrostriatal pathway accompanied by the presence of intracellular
cytoplasmic inclusions, termed Lewy bodies. Fibrillized a-synuclein forms
the major component of Lewy bodies. We reported a specific interaction
between rata-synuclein and tat binding protein 1, a subunit of PA700, the
regulatory complex of the 26S proteasome.
The COP9 signalosome (CSN) occurs in all eukaryotic cells. It is a regula-tory particle of the ubiquitin (Ub)⁄26S proteasome system. The eight sub-units of the CSN possess sequence homologies with the polypeptides of the
26S proteasome lid complex and just like the lid, the CSN consists of six
subunits with PCI (proteasome, COP9 signalosome, initiation factor 3)
domains and two components with MPN (Mpr-Pad1-N-terminal) domains.
Metabolically unstable proteins are involved in a multitude of regulatory
networks, including those that control cell signaling, the cell cycle and in
many responses to physiological stress. In the present study, we have deter-mined the stability and characterized the degradation process of some
members of the Gq class of heterotrimeric G proteins. Pulse-chase experi-ments in HEK293 cells indicated a rapid turnover of endogenously
expressed Gaq and overexpressed Gaq and Ga16
The 26S proteasome, a protein complex consisting of a 20S
proteasome and a pair of 19S regulatory particles (RP),
is involved in ATP-dependent proteolysis in eukaryotes.
In yeast, theRP contains six different ATPase subunits and,
at least, 11 non-ATPase subunits. In this study, we identi®ed
the rice homologs of yeast RP subunit genes from the rice
expressed sequence tag (EST) library.