Amplification and antibody expression by using plasmid set δ.

<p>Plasmids 1 (indicated) of plasmid set δ were co-transfected and selected by culture in the presence of 10 µg/ml blasticidin, the indicated concentrations of Mtx, and the absence of G418. The transfectant number (No.), Mtx concentration (nM), and the amplification method are indicated at the bottom of the figure. Transfectants CN61-3 and -1, and CN61-5 and -6, differ by whether the selection was started from 0 or 5 nM Mtx in the nucleotide-deficient medium. Cells reached confluence at the indicated number of days after transfection (Days a Trf). Cytogenetic structures were analyzed by FISH (A) (cw: chromowome width). Antibody expression was quantified by real-time PCR (B), and ELISA (C). Cells prepared for ELISA were grown in the presence (+) or absence (−) of 10 mM sodium butyrate (But). Error bars represent mean +/− S.D.