TABLE 2.

Half-lives of X-nsP4 in wild-type and mutant EF cells^a

N-terminal residue type	Residue	Half-life (mm)
		Wild-type EFs		UBR1−/− UBR2−/− EFs
		No treatment	UBR4RNAi D	No treatment	UBR4RNAi D	UBR4RNAi C	LucRNAi
Stabilizing	Met	75	>120	84	>120	>120	96
	Gly	>120		64	>120		88
Type 1	Arg	42	>120b	34	72	40	32
	His	36		50	>120		50
Type 2	Tyr	40	37	38	>120	56	32
	Phe	38		54	>120		39
	Leu	40		55	113		41
Type 3	Thr	61		52	99		48

^aHalf-life (t_0.5^0-60, min) of X-nsP4 between 0 and 60 min of chase was calculated as follows: t_0.5^0-60 = 50 (%) × 60 (min)/SD^0-60 (%). Subsequent decay (SD^0-60, %) denotes the ratio of the amount of a labeled X-nsP4 at 60 min of chase to that of the same labeled X-nsP4 at time zero. SD^0-60 = 100 − {[X-nsP4]₆₀/[X-nsP4]₀} × 100, where [X-nsP4]₆₀ was the amount of ³⁵S-labeled X-nsP4 at 60 min and [X-nsP4]₀ was as described in Table 1, footnote a.

^bThe amount of ³⁵S-labeled Arg-nsP4 at time zero in UBR4^RNAi EFs is significantly low (Fig. 5C and Table 1).