trp1-289 reversion help

[Shin Enomoto]

I am trying to revert trp1-289 in budding yeast strain S150B2 using a TRP1 
clone by transformation. 
 I used the EcoRI-BglII fragment to avoid the ARS1 for the transformation 
but I keep getting the TRP+ transformants that behave as plasmid 
transformants.  I am guessing that a TRP1-ARS1 circle is forming somehow,
since the plasmid tranformants appear to be relatively stable.

Is there a trick that I can use to avoid this? I have a mutant that I 
suspect is linked to TRP1 and would like to show this without outcrossing 
to another background.