I would agree with you that an internal control can only help (even if the
help is small) when comparing values within a cell line. However, when
comparing between cell lines I have a problem. There will be obvious
differences in the kinds and amounts of transcription factors between cell
lines. Thus, competition could present itself as a real problem. What I
also do is I compare different positive controls (SV40 versus RSV versus
CMV) just to make sure that there are not profound differences in the
activity of my positive control plasmid between cell lines.
Know these days I am tempted to simply express all the data as normalized
RLUs. Thus, the basic vector, positive control and experimentals are all
individually expressed. In this way, I leave it up the reader to interpret
the data since some express the results as percent of control and others
fold elevation over basic. Yet a third way that I am currently analyzing
is the percent of the maximal activity obtained with an experimental
promoter construct. I see this occasionally in the literature.
I should mention that I have done cotransfections (its been a while). I
recall that it made zero difference in the end analysis.
Anyway, I have escaped criticism thus far. Probably because my N's are
Anyone else out there who cares to debatethis issue??
The Love you take is equal to the Love you make--P. McCartney