Selection scheme for promoter regions. First, 300–600-bp genomic DNA fragments are subcloned into the BstXI sites in (A) retroviral plasmid pSKF-6. (B) The genomic DNA library is transfected into packaging cells that supply viral proteins encoded by gag, pol, and env, to convert DNA to the RNA virus. Target cells are infected with the viral library and screened by FACS for clones that drive the expression of the GFP reporter gene. Genomic DNA is prepared from the GFP-positive cells, and inserts are recovered by PCR amplification for sequencing and functional validation assays.
