Figure 2. Over-expressed DHFR does not aggregate inside the cell.
(A) DHFR fused to monomeric superfolder GFP was expressed from pBAD plasmid, and fluorescence of the cells was detected using a Zeiss Cell Observer microscope. Intracellular abundance of the fusion protein in the image shown was ~350 fold over chromosomally expressed DHFR. The fluorescence was uniformly spread over the cells, ruling out any substantial aggregation. Over-expressed fusion protein is not cleaved inside the cell, as both (B) anti-GFP and (C) anti-DHFR antibodies showed very minor fraction of cleaved proteins. In panels (B) and (C), lanes 1 to 5 represent different expression levels of DHFR-GFP fusion protein.