Expression of the recombined substrates. (a) Fluorescence microscopy of EGFP and DsRed expression. The four panels show expression of the DsRed (from unrearranged template) and rearranged EGFP gene products from inversion and deletion substrates in both 300-19P and WEHI231 cells. (b) Flow cytometric analysis of 4-week cultures of untransfected and transfected recombinant 300-19P (REC+) and WEHI231 (REC-) cell lines. The fold increase in number of EGFP-expressing cells was established by assigning an arbitrary value of 1 for untransfected cells.