Table 1. Effects of mutations in HIV-1 RNase H on sensitivity to RT inhibitors.

	AZT		d4T		ddI		3TC		EFV
	IC50 ± SE, μM	Fold inc.	IC50 ± SE, μM	Fold inc.	IC50 ± SE, μM	Fold inc.	IC50 ± SE, μM	Fold inc.	IC50 ± SE, μM	Fold inc.
Wild type	0.04 ± 0.004*	-	0.45 ± 0.04*	-	10.99 ± 1.94†	-	5.23 ± 0.98†	-	1.4 ± 0.33†	-
AZT-R	0.99 ± 0.36‡	23	1.08 ± 0.17‡	2.4	10.87 ± 2.7†§	None	>20†	>3.8	1.2 ± 0.16†§	None
D549N	0.52 ± 0.15†	12	1.06 ± 0.24‡	2.4	20.78 ± 2.76‡	1.9	8.85 ± 2.9†§	None	0.99 ± 0.3†§	None
H539N	7.96 ± 1.69†	185	4.51 ± 0.22†	10	ND		ND		ND
AZT-R+D549N	≈50‡¶	≈1,250	5.62 ± 1.55‡	12.5	9.94∥	None	>20∥	>3.8	0.89∥	None
WT+E478Q mixed virions	0.22 ± 0.07†	5.5	1.6 ± 0.6†	3.6	ND		ND		ND

IC₅₀ means and standard errors were calculated by using sigmaplot 8.0 as described in Methods. Fold increases (Fold inc.) were calculated only for statistically significant differences in IC₅₀ (P < 0.05, relative to wild type) by dividing the mutant virus IC₅₀ mean by the wild-type virus IC₅₀ mean for each drug. All infections were performed in duplicate, and the results were averaged. ND, not determined; -, not applicable.

^*IC₅₀ mean calculated based on measurements of 9-15 separate infections

^†IC₅₀ mean calculated based on measurements of two to four separate infections

^‡IC₅₀ mean calculated based on measurements of five to seven separate infections

^§IC₅₀ is not statistically different from the wild type (P > 0.03)

^¶For four of the five experiments, the highest drug concentration tested (10 μM) inhibited viral replication only by 10-30%; in one experiment, 50 μM AZT inhibited viral replication by 52%

^∥IC₅₀ mean calculated based on measurements of one infection