Minus-strand synthesis without segment L. Unlabeled RNA was added to procapsids along with labeled NTPs as described (12). Segment S alone or S and M together do not turn on minus-strand synthesis, but S, M, and L together do promote synthesis. Segment S and the transcript of pLM1827 (Fig. 1) do turn on minus-strand synthesis although the latter transcript contains no sequence of segment L. The pLM1827 transcript is 9.8 kb, which is close to the sum of M plus L, 10.5 kb. The transcript of pLM1822, which is 6.8 kb, does not turn on minus-strand synthesis. Lane 3, which has RNA of S, M, and L, is exposed for one-tenth the time of the other lanes. dsRNA, double-stranded RNA.