TABLE 1.

Amino acid substitutions in HIV-1 HXB2 protease with lowered susceptibility to indinavir discovered by screening of 12,000 HIV protease variants in E. coli^a

Variant	Substitution at the following position:														Reference(s)
	6 (W)b	14 (K)	24 (L)	43 (K)	53 (F)	54 (I)	55 (K)	63 (L)	64 (I)	70 (K)	82 (V)	85 (I)	90 (L)	91 (T)
DLH310							N						M		5
10K283	R														29
DLH1863	R														29
DLH3218	R				Y										29
DLH3519				T	L										17, 35
DLH7956														A	16
DLH8860													M		5
DLH8968			I					P		R					5
DLH9423		E										T
10K201									V		A				5
10K707						T									5
10K711					I

^aThe screening in E. coli described in the legend to Fig. 1 was used to search a library of HIV protease variants. A total 12,000 colonies were screened for HIV protease-dependent reverse transcriptase activity in the presence of indinavir. Those colonies which expressed indinavir-resistant HIV protease variants were retested, and for those that again showed resistance, the DNA was sequenced and the inferred amino acid substitutions were entered into the table. Amino acid substitutions indicated in boldface type coincide with resistance-conferring genes found in either clinical isolates resistant to indinavir (5) or mammalian cell culture resistance to other protease inhibitors (16, 17, 34). Note that one or two amino acid substitutions are sufficient to show significant decreased sensitivity to indinavir (also see Fig. 2 and 3). This is in marked contrast to the results of mammalian cell culture studies, in which the appearance of indinavir resistance requires at least three amino acid substitutions (5). 

^bLetters in parentheses indicate the native amino acids.