(A) Representative replication assay showing the accumulation levels of DI-73 (Y73, being the wt yeast plasmid counterpart) and its variants in yeast cells, as assessed by northern blot analysis. These replicons contained the same set of modifications that are shown in Figure 3A. (B) Representative replicase assembly assay showing the efficiency with which affinity-purified replicase (prepared from cells expressing the different DI-73 variants described above) copies an added DI-72(−) template in vitro. Terminally-initiated (ti) and internally-initiated (ii) products are indicated and the former was quantified. (C) Western blot showing levels of p33 present in the cells used for replicase preparation. Similar results were obtained when p92 levels were assessed (not shown). (D, E, F) are as described for (A, B, C), respectively, except that replication-defective forms of DI-73 (designated by the prefix “m”) were used in these assays.