Figure 7.

Plus-strand synthesis without segment L. Unlabeled RNA was added to procapsids along with labeled NTPs as described (12), but with 1 mM Mn²⁺ in addition to the 3 mM Mg²⁺ and 80 mM NH₄ acetate instead of 100 mM to promote plus-strand synthesis. In lane 1, segments L, M, and S served as templates for minus-strand synthesis (L, M, S) and for plus-strand synthesis (m, s). The plus strand of segment L is obscured by S. In lane 2 minus-strand synthesis occurs in the presence of intact segments S and M when packaged with segment L truncated at EcoRV (Fig. 1). In this case plus-strand synthesis does not occur as noted previously. Minus-strand synthesis is observed in lane 3 because Mn allows minus-strand synthesis without complete packaging (see Fig. 6). Plus-strand synthesis is seen in lane 4 for both segment S and the transcript of pLM1827, even though this transcript has no sequences of L. In lane 5 minus- and plus-strand synthesis is seen for the transcript of pLM1809 (Fig. 1), which has the pac site of S and the entire genetic complement of Φ6 and a size of 13.5 kb. Lanes 1 and 2 were exposed for one-tenth the time of the other lanes. dsRNA, double-stranded RNA; ssRNA, single-stranded RNA.