% of G418-resistant colonies expressing beta-gal

Kevin A. Mulcahy K.Mulcahy at sheffield.ac.uk
Thu Jan 2 09:47:49 EST 1997

I have recently stably-transfected a melanoma cell line with a ß-gal 
reporter plasmid (pCR3-ß-gal). However, following 2 weeks of 
G418-selection only one out of approximately 100 G418-resistant 
colonies expressed ß-gal!

Since: (1) the G418 concentration was the minimal dose which killed 
all untransfected cells in a 2 week assay and (2) transient 
transfections performed at the same time (and same conditions) as the 
stable transfections indicated that 10-20% of the cells expressed 
ß-gal, I cannot understand why only 1% of the stably-transfected 
colonies expressed ß-gal.

I'd be grateful if anyone has any comments or ideas?

Many thanks,

Kevin Mulcahy.

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