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YAC stability

Andrei Popov ANDREI.POPOV at bbsrc.ac.uk
Tue Nov 7 16:18:18 EST 1995

>Since the main problem with using YACs is their susceptibility to
>rearrangement, does anyone have any ideas how to propagate YACs
>stabily?  Does the problem come from the cloning, the propagation, or
>something else?  Would it be possible to construct a yeast strain that
>would allow for the propagation of stable YACs?  Any ideas,
>suggestions, or references would be greatly appreciated.
>Dubear Kroening
>dubear at whitewater.chem.wisc.edu  

Hello Dubear,

I always thought that the main problem using YACs is to find
the right one :-)
There are several problems:
1. chimaerism, which comes from recombination between two
  DNA pieces shortly after ligation mixture transformation
   into spheroplasts
2. unstability because of the presence of the recombinational hotspots
   in the cloned DNA

3. presence of YACs (originally cloned as one copy per cell)
  in several  copies even in haploid hosts. This is best illustrated
   on EtBr stained gels when you see the YAC band much brighter
    than that of the host chromosomes. The more copies you have in one cell
     the greater are the chances of recombination between them
    producing "bastard" , smaller or bigger YACs.

As to how stabilize YACs, there were a couple of papers on YAC-
libraries in RAD52 mutants which indeed showed low level
of chimerism. You can look also at paper in NAR 1994 22 p 4154
for more details.


Andrei Popov

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