Sts1 can overcome the loss of Rad23 and Rpn10 and represents a novel regulator of the ubiquitin/proteasome pathway.

A rad23Delta rpn10Delta double mutant accumulates multi-Ub proteins, is deficient in proteolysis, and displays sensitivity to drugs that generate damaged proteins. Overexpression of Sts1 restored normal growth in rad23Delta rpn10Delta but did not overcome the DNA repair defect of rad23Delta. To understand the nature of Sts1 suppression, we characterized sts1-2, a temperature-sensitive mutant.

Proteasome-mediated degradation of cotranslationally damaged proteins involves translation elongation factor 1A.

Rad23 and Rpn10 play synergistic roles in the recognition of ubiquitinated proteins by the proteasome, and loss of both proteins causes growth and proteolytic defects. However, the physiological targets of Rad23 and Rpn10 have not been well defined. We report that rad23Delta rpn10Delta is unable to grow in the presence of translation inhibitors, and this sensitivity was suppressed by translation elongation factor 1A (eEF1A).

Investigating the importance of proteasome-interaction for Rad23 function.

Rad23 contributes to diverse cellular functions that include DNA repair, stress response and growth control. An amino-terminal ubiquitin-like (UbL) domain in Rad23 interacts with catalytically active proteasomes and internal sequences bind multi-ubiquitinated proteins. Rad23 regulates the assembly of substrate-linked multi-ubiquitin chains, promotes efficient degradation of model substrates, and plays an overlapping role with the proteasome subunit, Rpn10.

The DNA repair protein rad23 is a negative regulator of multi-ubiquitin chain assembly.

Rad23 is a nucleotide-excision repair protein with a previously unknown biochemical function. We determined that yeast and human Rad23 inhibited multi-ubiquitin (Ub) chain formation and the degradation of proteolytic substrates. Significantly, Rad23 could be co-precipitated with a substrate that contained a short multi-Ub chain.

Evidence for an interaction between ubiquitin-conjugating enzymes and the 26S proteasome.

The targeting of proteolytic substrates is accomplished by a family of ubiquitin-conjugating (E2) enzymes and a diverse set of substrate recognition (E3) factors. The ligation of a multiubiquitin chain to a substrate can promote its degradation by the proteasome. However, the mechanism that facilitates the translocation of a substrate to the proteasome in vivo is poorly understood.

Pleiotropic defects caused by loss of the proteasome-interacting factors Rad23 and Rpn10 of Saccharomyces cerevisiae.

Rad23 is a member of a novel class of proteins that contain unprocessed ubiquitin-like (UbL) domains. We showed recently that a small fraction of Rad23 can form an interaction with the 26S proteasome. Similarly, a small fraction of Rpn10 is a component of the proteasome.

Rad23 links DNA repair to the ubiquitin/proteasome pathway.

Rad23 is an evolutionarily conserved protein that is important for nucleotide excision repair. A regulatory role has been proposed for Rad23 because rad23 mutants are sensitive to ultraviolet light but are still capable of incising damaged DNA. Here we show that Rad23 interacts with the 26S proteasome through an amino-terminal ubiquitin-like domain (UbL[R23]).