Figure 1. Inducible, barcode short-hairpin RNA (shRNA) library screen strategy for genes controlling cancer cell proliferation and survival. Infection of an shRNA retroviral library into a cancer cell line produces a “cellular library” with each cell carrying one or more shRNAs. Each shRNA is tagged by a known, unique barcode. Infected cells are divided into two subpopulations, one induced for expression of shRNAs and the other serving as the control. The inducibility of the shRNA library is important to prevent the loss of shRNA species that are acutely deleterious to infected cells. A time-dependent selective pressure is applied and genomic DNA fragments carrying the barcode representing each shRNA from each subpopulation are amplified by PCR, labeled with different fluorescent dyes, and cohybridized to a microarray containing complementary barcode oligonucleotides. The microarray is scanned and the relative abundance in the two subpopulations of an shRNA targeting a gene that influences cell proliferation or survival can be quantified.