Blue/white colony selection problem.

G Selvarani medp3056 at
Fri Sep 9 05:40:50 EST 1994

Wises Namwat - SCMI - 3636183 (gscwnw at MUCC.MAHIDOL.AC.TH) wrote:
: Hello  netter,
:   	I have some problems in transformation technique. pGEM7(+/-) was 
: used as a vector for the DNA insert, this ligated product was then 
: transfect into competent E. coli(DH5alpha). Blue/white colonies 
: growing on amp&x-gal plate can be use for selection the success insertion 
: clone, the white colonies. Theoritically, the white colonies must be 
: bigger than the blue ones. But the smaller white colonies always appear 
: around the blue colony. These smaller clones contain the different size 
: of plasmid. Does anybody know what are these smaller colonies, and where 
: does their plasmid come from?
: 	Thanks in advance.
: ----------------------------------------------------------
: Wises namwat             email: gscwnw at
: Dep. Microbiology,       Tel.66-02-2461358-74 Ext.4611    
: Fac. Science,
: Mahidol University,
: Bangkok, Thailand.
: ----------------------------------------------------------
We've encounted such things. In fact, if we spread our plates too early 
in the day the sattelite colonies(the little one around the big colony) do 
appear.Apparently the satellite colonies (competent colony)grows 
surrounding the real colonies ones the ampicillin runs out around the area
they do not contain any insert or plasmid. dna appears with extractions 
maybe due to contamination of chromosomal dna.
that,s all.

good luck.

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