The present invention relates to methods and compositions for the elucidation of
mammalian gene function. Specifically, the present invention relates to methods and compositions for improved mammalian
complementation screening, functional inactivation of specific essential or non-essential mammalian genes, and identification of mammalian genes which are modulated in response to specific stimuli. In particular, the compositions of the present invention include, but are not limited to, replication-deficient retroviral vectors, libraries comprising such vectors, retroviral particles produced by such vectors in conjunction with retroviral packaging
cell lines, integrated
provirus sequences derived from the retroviral particles of the invention and circularized
provirus sequences which have been excised from the integrated
provirus sequences of the invention. The compositions of the present invention further include novel retroviral packaging
cell lines.