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. 1997 Nov 11;94(23):12503–12508. doi: 10.1073/pnas.94.23.12503

Figure 1.

Figure 1

Spontaneous generation of [URE3]. Strain 4444–3A (MATα his3 ura2 leu2 ure2::URA3) was transformed with p645 (YEp351G-URE2; ref. 8) in which URE2 is under control of the GAL1 promoter on a LEU2 plasmid. The expression of Ure2p in this strain on galactose made it unable to use USA in place of uracil. Colonies that grew on USA were candidates to have had spontaneous generation of [URE3]. The USA+ trait of colonies U15 and U19 was cytoducible to the URE2 recipient strain 3748, showing that U15 and U19 carried [URE3]. Colonies U15 and U19 were streaked for single colonies on GalUraHis plates containing 5 mM guanidine HCl. Each of nine Leu+ single colonies of both U15 and of U19 were unable to grow on USA. Colonies of U15 and U19 grown on Dex + Ura + His (to shut off Ure2p synthesis) also had become unable to grow on Gal + USA + His.