insert-positive blue cols

[Thomas J Radosevich]

In <1993Jan21.090729.79 at ebc.ee> mspeek at ebc.ee (Mart Speek) writes:


>Hi Netters;

>I would like to know whether anyone has encountered problems
>in traditional blue/white colony or plaque screening procedures
>(beta galactosidase assay) when sorting out (non)recombinant
>clones. My question is :-( Could relatively long inserts (>0.5kb)
>sometimes give rise blue (beta gal+) clones? How is it possible?
>Any theoretical or practical solutions (incl refs) to this 
>particular problem are welcome.

>M. Speek

>mspeek at ebc.ee (ESTONIA)

I've had blue positives twice--one of 143 bp and the other 550 bp.  For the 
143 I unsuccessfully checked white colonies for quite some time.  Eventually
I checked blue colonies and they were all positive.  Now, whenever I clone a
small fragment, I always throw a few blue colonies in the first batch of
minipreps.  (BTW, these were bluescript/XL1 blue transformations)

Hope it helps--Tom Radosevich