TABLE 2.

Slippery-site SARS-CoV sequences^a

Slippery-site sequence	% −1 PRF	SD	Plaque size	TCID50
U UUA AAC (WT)	14.40	2.35	+++	4.53
U UUU UUC	12.24	2.41
A AAT TTA	4.93	1.56
U UUU UUU*	4.88	1.31	++	<1
A AAA AAC	4.40	1.02
G GGA AAC	3.97	0.70
G GGU UUA	3.57	0.74
U UUA AAU	3.23	1.48
U UUA AAA	2.81	0.82
A AAA AAU*	2.33	0.55	+	<1
C CCA AAC	2.21	0.81
G GGU UUC	1.94	0.83
U UUA AAG	1.72	1.24
G GGU UUU	1.67	0.67
U UUG AAA	0.70	0.19
G GGU UUG	0.58	0.13
U UUG AAC*	0.15	0.03	−	ND

^aSlippery-site SARS-CoV sequence mutants and incoming reading frames are indicated by spaces. *, slippery sites incorporated into infectious clones. −1 PRF efficiencies and standard deviations were measured in Vero cells as previously described (60). The plaque sizes of infectious clones are indicated by the number of plus signs. The TCID₅₀ (log₁₀/10 viral genomes) is the average of six measurements. The lower limit of the assay (1 log₁₀) is 1.