Correspondence

Ongoing transcription in vitro of Tomato spotted wilt virus (TSWV) has previously been demonstrated to require the presence of reticulocyte lysate. This dependence was further investigated by testing the occurrence of transcription in the presence of two translation inhibitors: edeine, an inhibitor that still allows scanning of nascent mRNAs by the 40S ribosomal subunit, and cycloheximide, an inhibitor that completely blocks translation including ribosome scanning. Neither of these inhibitors blocked TSWV transcription initiation or elongation in vitro, as demonstrated by de novo-synthesized viral mRNAs with globin mRNA-derived leader sequences, suggesting that TSWV transcription in vitro requires the presence of (a component within) reticulocyte lysate, rather than a viral protein resulting from translation. Transcription of segmented negative-strand RNA viruses is initiated by a mechanism known as cap snatching, in which the viral polymerase cleaves a host mRNA generally at 10–20 nt from its 59-capped end and uses the resulting leader to prime virus transcription. This also applies to Tomato spotted wilt virus (TSWV), the type species of th