Table 1.

Nuclear ubiquitin-proteasome pathways for degradation of protein quality control (PQC) substrates in yeast.

	E3 Ubiquitin Ligase	E2 Involved	Nuclear PQC Substrates		Degradation Signal
INMAD
	Asi1-Asi3	Ubc6 and Ubc7 [31] Ubc4 and Ubc7 [30,34]	nuclear proteins:	Stp1 and Stp2 [31,37]	nuclear RI region (amphipathic helix) [31,37]
			integral INM 1 proteins:	INM-mislocalized [31,40]	transmembrane domains [34]
				orphan subunits and lone proteins [34]
				ts2 mutants [34]
				other [30,31,40]
	Doa10	Ubc6 and Ubc7 [41]	nuclear proteins:	Matalpha2 [41]	amphipathic helix [50]
				Ndc10-2 (ts) [43]	amphipathic helix and hydrophobic region [53]
			integral INM 1 proteins:	Asi2 [47]	not determined
				Mps2-1 (ts) [43]	not determined
	APC/C Cdh1	Ubc7 [58]	integral INM 1 protein:	Mps3 [58]	nucleoplasmic KEN-box and D-box-like sequences [58]
Nuclear
	San1	Ubc1 or Ubc3/ Cdc34 [62,63]	nuclear proteins	ts 2 mutants of nuclear proteins [62]	exposed hydrophobicity [66]
				truncated proteins [66,70,76]
				artificial substrates and other mutants [66,67,70,71,72,73,75,76,77]

¹ INM—inner nuclear membrane, ² ts—temperature sensitive.