blue centres of white colonies

Marci Swede ms5h+ at
Fri Apr 24 13:15:22 EST 1992

>I use pGEM3Zf(+) as a convenient cloning vector for our cDNA work.
Recently, I'
>ve found
>amongst all white and all blue colonies, also a variety of white
colonies with 

I use a lacZ gene fusion in yeast frequently.  Often I will see this
same effect when the colony I use for replicating onto the indicator
plate is quite thick (and therefore the resulting print is heavy).  The
replicated patch will appear blue, but then will grow white around it. 
In our fusion, when our gene is repressed the colonies are white, so it
is easy to distinguish the false blue after the cells begin to grow, and
grow white.  I'm not sure that this is completely relevent, but I hope
it helps.

Marci Jan Swede
CMU Biology

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