petite transformant

[Sandra Bond]

James Campanella asked for methods for improving the growth rate of a 
petite transformant that uses Ura as the selectable plasmid marker and
is also a Phe auxotroph.  (1) Perhaps the best way to deal with this 
problem would be to find a non-petite recipient strain and retransform,
if necessary replica-plating the original transformants to YEP-glycerol
or YEP-ethanol to identify non-petite transformants (or possibly 
selecting grandes by using glycerol or ethanol instead of glucose in the
transformation plates, but that might trash the transformation itself, I
don't know).  (2) If diploidy would not be a problem, you could mate the 
petite transformant to a non-petite strain with suitable markers to get 
a non-petite diploid (and, in theory, you could then sporulate the 
diploid to recover haploid non-petites if necessary).  (3) You might be 
able to perk up the growth rate of the petite strain by adding 
ergosterol at 20 milligram per liter, and 0.5% v/v Tween 80 (if it 
works, let me know!).

Robert A. Preston
Pathology Dept.
UPMC Pittsburgh
rapr at med.pitt.edu