Abstract: The present invention is directed to methods for performing negative selection assays leading to the identification of cytostatic or cytotoxic agents that cause a lethal phenotype. The invention is useful also for evaluation of conditional cytotoxicity and cell-specific cytotoxicity.

Abstract: Methods for identifying nucleic acid sequences that affect a cellular phenotype are disclosed. The method uses a reporter gene whose level of expression correlates with the phenotype in conjunction with a method or device for measuring the level of reporter expression. An expression library is introduced into the cells, and those cells exhibiting changes in reporter expression level are selected. Expression library inserts from the selected cells are isolated, thereby providing a sub-library enriched for sequences that affect the phenotype reflected by the reporter. Further rounds of sub-library introduction and cell selection may be carried out to provide additional enrichment. Sequences identified using this method may be used to ascertain the identity of additional molecules involved in generating the cellular phenotype.

Abstract: Methods and compositions for peptides or protein fragments displayed on scaffolds and libraries of sequences encoding peptides or protein fragments displayed on scaffolds that permit the properties of the library to be easily and quantitatively monitored are disclosed. The scaffold is a protein that is capable of emitting light. Thus, analysis of the expression of individual members of the library when they are expressed in cells may be carried but using instruments that can analyze the emitted light, such as a flow sorter (FACS), a spectrophotometer, a microtitre plate reader, a CCD, a fluorescence microscope, or other similar device. This permits screening of the expression library in host cells on a cell-by-cell basis, and enrichment of the library for sequences that have predetermined characteristics.