Yes, of course !
We also have such experience with ES clones transfected with EGFP-1
It´s natural and well known "positional effect" due to
random insertion of EGFP under some active cells promoters.
Moreover, it´s a basis of known "genes trap"method to reveal
some actually active genes (up to now, though, applied mainly with LacZ
Institute for Neurophysiology
University of Cologne
50931 Cologne, Germany
e-mail:ek at physiologie.uni-koeln.de