Fig. 2.

Complementation of DHFR-negative phenotype in a mammalian system. Cell counts of transfected CHO DG44 cells after switching cells to media without supplements. Cells were counted after 1, 5, and 12 d in complementation media. Cells transfected with either DHFR (A) or DHFRL1 (B) had some cell death on day 5; however, by day 12 both sets of cells had recovered and were growing well in the complementation media. The cells transfected with DHFR grew more quickly than those transfected with DHFRL1. (C) Cells transfected with the empty vector alone did not survive without supplements.