Ligation mystery

Steven Sullivan sullivan at
Thu Jul 17 21:53:12 EST 1997

Has this ever happened to you?

I set up several ligations, using gel-purified double-digested DNA (the
vector DNA had even been dephosphorylated to ensure low background,
although this shoudl not be necessary if the double digest was complete).
After transformantion and growth overnight on LB/amp plates, the
vector-only control plates were blank as expected.  The experimental
plates had varying abounts of colonies, depending on the insert . However,
*none* of these colonies had inserts, as assessed by PCR or miniprep.  (I
should perhaps mention taht the vectors pCS2+ and pCS2+MT, are not
blue/white selectable. )

I don't understand how empty plasmids can religate and grow on the
experimental plates but not on the control.

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