Synthesis of novel products in vitro by an RNA-dependent RNA polymerase

RNA-dependent RNA polymerase from turnip crinkle virus-infected turnip transcribes both strands of a virus-associated satellite RNA, sat-RNA C (356 bases), in vitro. While both plus- and minus-strand sat-RNA C can direct the synthesis of full-length complementary-strand products, transcription of minus-strand RNA also generates two non-template-sized products, L-RNA and S-RNA (C. Song and A. E. Simon, Proc. Natl. Acad. Sci. USA 91:8792-8796, 1994). Here we report that synthesis of L-RNA and S-RNA results from terminal elongation of the 3' end of the template. L-RNA has a panhandle structure and is composed of minus-strand template covalently linked to newly synthesized RNA complementary to its 5' 190 bases. S-RNA is composed of template covalently linked to its full-length complementary strand. All minus-strand templates tested yielded S-RNA. However, synthesis of L-RNA was affected by deletion of the 3' end of the minus-strand template or several internal regions and base alterations near the 5' end or in an internal sequence immediately upstream from the template-product junction that could potentially form a heteroduplex with the 3' end. Furthermore, mutations that disrupted or restored a stem-loop involved in RNA recombination in vivo affected the level of L-RNA produced in vitro, suggesting that the mechanisms for intramolecular formation of panhandle RNAs and intermolecular RNA recombination involve similar features.