blue colonies

Wendy Bedale bedal001 at
Tue Apr 25 17:38:58 EST 1995

In article <3njeac$dc8 at>, ez022056 at
(Edward Wang) wrote:

> I am currently doing PCR cloning using the Promega pGem-T system.  
> Everything was working fine, and I was getting several hundred : 5 White 
> to blue ratio, using Stratagene's super competent (10^9 efficiency) XL1 
> Blue cells.  Because of the high cost, I switched to Promega's JM109 
> (10^8 efficiency).  Now, my plates have lots of blue colonies : very few 
> white colonies.  Does anyone know any explaination for this?
> Also, we are trying to od Nrothern blots with probes made from 
> differentialy displaying fragments (DD-RTPCR), but so far with no luck 
> (nothing shoing on the blot).  Has anyone else had any similar problems, 
> and perhaps even the solution to the problems?  Thanks in advance.

Is this a TA cloning kit?  If so, maybe your vector has lost its T-tails
over time- I know that can happen with the Invitrogen TA cloning vector.

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