Co-introduction of two plasmids with the same CEN element?

Ashok Aiyar aiyar at
Thu Oct 28 01:18:30 EST 1999

I have seen several studies where two ARS/CEN plasmids that share 
the same ARS element but different CEN elements (and selectable
markers) are maintained together in S. cerevisiae.

I have tried to co-introduce two plasmids into the same haploid
strain of S. cerevisiae.  So far I have been unable to select for
transformants that contain both plasmids.  Plating the same
transformations under conditions that select for a marker on one 
plasmid or the other works.

Both these plasmids contain the same CEN element (CEN3).  Obviously
diploid yeast have no problem having two copies of CEN3.  A casual
sequence analysis indicates that all CEN elements have very similar

So has anyone else encountered a problem in "co-maintaining" two 
plasmids that contain the same CEN element.  I have just tried to
introduce the two plasmids sequentially into the strain -- and 
should know if that has worked 2 - 3 days.


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