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. 2007 Jan 24;2(1):e175. doi: 10.1371/journal.pone.0000175

Figure 6.

Figure 6

Position-effect blocker activity of the XB fragment. (A) Constructs introduced into the NIH3T3 cell line. Construct I (top) contains a CAGGS promoter-driven fluorescent protein (Venus) and a neomycin-resistance gene, enabling G418 selection of stable transformant colonies of transfected NIH3T3 cells. Construct II (bottom) is organized similarly, except it contains XB blocker fragments bordering both sides of the Venus expression marker gene. (B) Experimental scheme illustrating the transfection scenario. Stable transformants of both constructs were selected using G418. Colonies were maintained in culture for one year. We selected samples from each colony after 1, 6, and 12 months for FACS analyses. (C) Fluorescence assessment of 12 colonies harboring either Construct I or Construct II. Fewer fluorescent cells were observed in colonies lacking the XB fragment, while numerous fluorescent cells were observed in colonies harboring the XB fragment, indicating that the XB construct (Construct II) maintained Venus expression.