>We have a pYAC4 derived YAC, and we would like to delete
>the URA3 marker on the right arm so that we can use URA3
>to replace a gene within the YAC. Has anyone out there tried
>growing pYAC4 derived YACs without selection for one or
>both arms? How stable is it?
YAC ARM STABILITY APPEARS TO BE INDEPENDANT FROM
SELECTIVE MARKERS. SOMETIMES YAC-CONTAINING YEAST
ARE GROWN IN YPD AND THE ONLY RESULT IS THAT SOME
PROPORTION OF CELLS LOOSE THE YAC.
AFTER TRANSFORMATION WITH pYAC-DERIVED LIGATION MIXTURES
YACS ARE SELECTED IN AGAR W/O URA BUT WITH TRP, BECAUSE
TRP1 GENE IN pYAC4, pYAC-RC.... CONTAINS TRUNCATED PROMOTER.
HOWEVER IN YOUR CASE I WOULD HAVE USED LYS2 OR ADE2 GENE
FOR SELECTION (IF YOUR HOST STRAIN IS LYS AND ADE AUXIOTROPHIC)