Poltergeist in S. marcescens strain

mrege at cnbvx3.cnb.uam.es mrege at cnbvx3.cnb.uam.es
Tue Sep 7 10:31:48 EST 1993

Thank you, Mike, for the references.

The misterious observation consists in the following:

When transforming a S. marcescens strain (28b) with recombinant plasmids 
containing homologous sequences or lac operon from E. coli, we
have consistently observed a extremely low efficiency of transformation.
(We are using electroporation at the higher voltage). The few transformants
obtained do present plasmids lacking some regions; some restriction sites
had been removed and, surprisingly, some other appeared. This is not a 
classical recombination event, because it seems to affect non-contiguous
regions. Furthermore, it only affects a small region of our insert, 
because plasmids lacking this region are not affected, nor vectors alone.

We are working with a small piece of chromosomal DNA encoding a bacteriocin,
so we don't know if this is a specific mechanism or a more general one.
It's amazing the fact that it is also observed in vectors containing the
lac operon, and the strange observation of an apparent 'exchange' 
phenomenon. That's what led us to think in a restriction/modification
mechanism implicated.

Funny thing, isn't it?

Josefina Enfedaque
Dep. Microbiologia
Universitat de Barcelona (Spain) 

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