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There is no way that the GFP will EVER be as sensitive as lacZ/FDG. We
were able to run the FACS-Gal assay down to 5 molecules of lacZ per
cell (!). Typically, at least 20-30 are needed for minimal detection
in most cell lines; by the time you get to 100 per cell, you have a
reasonably bright system!
100 GFP's are unlikely to be detectable in a single cell.
That said, GFP is, however, quite useful. Especially the more recently
published mutants which are considerably "brighter"... with a
reasonable strong promoter, expression can be easily detected with
positively-expressing cells 1-2 orders of magnitude above autofluorescence.
Dr. Darley is correct: the catalytic activity of lacZ, which allows
single enzyme molecules to generate thousands of fluors, gives that
system an amplification advantage for sensitivity that will not be
overcome by GFP.
mr
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