TABLE 1.

17b induction and envelope fusion function for envelope glycoproteins containing changes in the variable loops^a

gp120 region	Envelope glycoprotein	Virus entry	Syncytium formation	Induction of 17b binding
V1/V2	Wild-type	1	1	4
	152/153 GE/SM	0.33	ND	3.1
	168 K/L	0.22	ND	3.4
	177 Y/F	0.34	0.06	2.5
	178 K/E	0.83	0.66	5.1
	179 L/V	0.55	0.35	3
	179/180 LD/DL	0.35	ND	2.9
	181 I/M	1.56	0.56	3.3
	191/192/193 YSL/GSS	0.06	ND	3.1
V3	298 R/G	0.82	0.43	3.6
	306/308 RR/SH	0.07	0.21	3.1
	308 R/H	0.13	0.14	3
	313 P/S	0.34	0.42	3.4
	313/315 PR/LG	0.03	0.06	3.8
	314 G/Q	0.57	0.31	3
	314 G/W	0.08	0.07	2.9
	315 R/G	0.04	0.07	3.9
	MT33+1	0.04	0.06	3.8
C4	420 I/R	0.15	ND	1.8
	475 M/S	0.73	ND	2.5

^a17b induction is the ratio of 17b bound in the presence of sCD4 (1 μg/ml) to 17b binding in the absence of sCD4. Syncytium-forming ability was determined by cocultivation of envelope glycoprotein-expressing COS-1 cells with CD4⁺ SupT1 cells and is expressed relative to the wild-type level of 1. Virus entry was measured by using an envelope complementation assay described in Materials and Methods. Values represent virus entry relative to the level of entry by viruses with the wild-type envelope glycoprotein. The values presented for 17b binding, syncytium formation, and virus entry are representative of at least three experiments except for a subset of the virus entry values, which are the means of two experiments. ND, not determined.