A bacteriophage lambda-based genetic screen for characterization of the activity and phenotype of the human immunodeficiency virus type 1 protease

Human immunodeficiency virus type 1 (HIV-1) resistance to antiretroviral dr ugs is the main cause of patient treatment failure. Despite the problems as sociated with interpretation of HIV-1 resistance testing, resistance monito ring should help in the rational design of initial or rescue antiretroviral therapies. It has previously been shown that the activity of the HIV-1 pro tease can be monitored by using a bacteriophage lambda-based genetic assay. This genetic screening system is based on the bacteriophage lambda regulat ory circuit in which the viral repressor cI is specifically cleaved to init iate the lysogenic to lytic switch. We have adapted this simple lambda-base d genetic assay for the analysis of the activities and phenotypes of differ ent HIV-1 proteases. Lambda phages that encode HIV-1 proteases either from laboratory strains (strain HXB2) or from clinical samples are inhibited in a dose-dependent manner by the HIV-1 protease inhibitors indinavir, ritonav ir, saquinavir, and nelfinavir. Distinct susceptibilities to different drug s were also detected among phages that encode HIV-1 proteases carrying diff erent resistance mutations, further demonstrating the specificity of this a ssay. Differences in proteolytic processing activity can also be directly m onitored with this genetic screen system since two phage populations compet e in culture with each other until one phage outgrows the other. In summary , we present here a simple, safe; and rapid genetic screening system that m ay be used to predict the activities and phenotypes of HIV-1 proteases in t he course of viral infection and antiretroviral therapy. This assay respond s appropriately to well-known HIV-1 protease inhibitors and can be used to search for new protease inhibitors.