tokens: p53 cDNA was amplified by PCR and cotransformed into yeast , IG397 Ade2 strain , together with either pRDI - 22 vector for p53 - standard assay or pFW35 and pFW34 plasmid for 5 ' or 3 ' split assay , respectively , carrying the ADE2 open reading frame under the control of a p53 - responsive promoter ( 20 ) .