TABLE 1.

Y472A and Y473S revertants^a

Construct	Plaqueb	Revertant plaqueb	Reversionc
WT(Y472Y473)	Large
Y473S  TAC → AGC	—	Large	AGC→ TAC
(Tyr → Ser)			(Ser → Tyr) (3)
Y472A TAC → GCC	—	Large/	GCC—GCC
(Tyr → Ala)		Small	(Ala—Ala) (4)

^aRevertants were isolated by passaging of the culture medium (1/4 volume) from transfected Vero cells with mutant RNAs to a new monolayer of Vero cells. After incubation for 6 days at 37°C, the culture medium was harvested and passaged in the same manner. After five passages, plaque assay of the culture medium was performed to determine the formation of plaques and virus titers. Viral RNA was extracted from the viruses in passage 5 and was used for cDNA synthesis and PCR amplification and cloning. 

^bPlaque assay was performed and the plaques are shown in Fig. 2. 

^cOnly the E1 cytoplasmic domain coding region was sequenced; numbers indicate numbers of sequenced DNA clones.