High frequency of yeast transformation by plasmids carrying part of entire 2-μm yeast plasmid

Abstract By using two chimeric plasmids containing yeast ura3 gene and 2-μm yeast DNA linked to the bacterial plasmid pCR1, yeast transformation of a high frequency has been achieved. The first plasmid is such that the 2-μm DNA part, in which the ura3 gene is incorporated, can be removed in one step and thus the 2-μm— ura3 sequence can be considered as a “transposable” block. In contrast, the second one bears the entire 2-μm plasmid and the ura3 gene is inserted in the bacterial plasmid part. As shown through hybridization experiments and genetic studies, the ura3 gene was maintained as a cytoplasmic element. Plasmids recovered from the yeast transformants were used to transform Escherichia coli . Their analysis by Eco RI showed that in many cases the vector had recombined with the endogenous 2-μm DNA of the recipient strain. The specific activity of orotidine 5′-monophosphate decarboxylase (coded by ura3 ) in yeast transformants was 10- to 30-fold higher than in the wild type.