Table 2.

Specific amino acid residues in the predicted R5 and X4/R5X4 V3 regions.

Residues in V3a	R5, n = 97	X4/R5X4, n = 28	P value
T12	12 (12.4%)	11 (39.3%)	0.0040
R13	31 (32.0%)	18 (64.3%)	0.0037
V21	15 (15.5%)	14 (50.0%)	0.0005
K33	22 (22.7%)	21 (75.0%)	<0.0001
T12 + R13	6 (6.2%)	11 (39.3%)	<0.0001
T12 + K33	6 (6.2%)	10 (35.7%)	0.0002
R13 + V21	6 (6.2%)	13 (46.4%)	<0.0001
R13 + K33	17 (17.5%)	16 (57.1%)	0.0001
V21 + K33	3 (3.1%)	13 (46.4%)	<0.0001
T12 + R13 + V21	1 (1.0%)	7 (25.0%)	0.0001
T12 + R13 + K33	5 (5.2%)	10 (35.7%)	0.0001
T12 + V21 + K33	2 (2.1%)	7 (25.0%)	0.0004
R13 + V21 + K33	2 (2.1%)	12 (42.9%)	<0.0001
T12 + R13 + V21 + K33	1 (1.0%)	7 (25.0%)	0.0001

K, lycine; R, argenine; R5, CCR5 tropic virus; R5X4, CCR5 and CXCR4 dual-tropic virus; T, threomine; V, valine; X4, CXCR4 tropic virus.

^aAmino acid residues were numbered according to the HXB2 V3 sequence.