Yeast linear plasmids with T2AG3 telomeres: TEL+CEN antagonism and genetic and molecular stability

A linear plasmid containing ARS1, CEN4, and 48 bp of vertebrate (T2AG3) telomeric sequences at each end was used to transform Saccharomyces cerevisiae. Only circular plasmids that had lost the centromere and had retained the T2AG3 sequences were obtained, indicating that the vertebrate T2AG3 sequences and the yeast CEN4 could not be simultaneously present in this vector. This hypothesis was verified by removing the CEN4 sequence from the construct. In fact, the resulting transformants contained two classes of efficiently replicating linear plasmids: one of the expected size and one about twice as large. During subsequent growth, plasmids of the former, but not latter, class were subjected to concatemer formation. This can best be explained by recombination events involving the T2AG3 sequences at the ends of the molecule, since very similar centric and acentric linear plasmids bearing Tetrahymena telomeric ends replicated faithfully.