Actually, this system can be used to repress or induce, depending on
whether you add or subtract tet. Also, there are constructs with the
vp-16 domain attached, so its activity is reversed. The concept of
inducibility is problematic. If the background is zero - it follows
that even the slightest expression can be called infinately inducible.
Also, my impression is that the main difference between 5x and 1000x
induced systems is the reduction in background - if you look at the
absolute level of expression it is similar. My conclusion is from
3-4 papers and not comprehensive. If someone can correct me, please do.
pw at cubsps.bio.columbia.edu