blue colonies

[Wendy Bedale]

In article <3njeac$dc8 at mark.ucdavis.edu>, ez022056 at bullwinkle.ucdavis.edu
(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.