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Nat Cell Biol. 2000 Sep;2(9):601-8.

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

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Department of Biochemistry, Robert Wood Johnson Medical School-UMDNJ, 675 Hoes Lane, Piscataway, New Jersey 08854, USA.


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. The UV sensitivity of rad23Delta was reduced in mutants lacking the E2 enzyme Ubc4, or the multi-Ub chain-promoting factor Ufd2. These studies suggest that the stability of proteolytic substrates is governed by the competing action of multi-Ub chain-promoting and chain-inhibiting factors. The stabilization of DNA repair and stress factors could represent an important biological function of Rad23.

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