Fig. 1. SeV RNA synthesis from wild-type and promoter-variant viruses. The dotted rectangle encloses a flow diagram of viral RNA synthesis. [–] genomes and [+] antigenomes are shown as a series of three boxes that are not drawn to scale; the leader (le) region in white (nucleotides 1–55), the train of six mRNAs in gray (abbreviated as N/L, nucleotides 56–15 329) and the trailer (tr) region in black (nucleotides 15 330–15 384). Nucleotides 31–42 of the black trailer region (or more properly nucleotides 15 342–15 353 of the genome) are highlighted with a white border. Vertical arrows indicate the flow of viral RNA synthesis. Genome replication requires a continuous supply of newly made N protein subunits, in contrast to the synthesis of le RNA, mRNAs and tr RNA. The sequence exchanges in the leader regions of SeV-GP1–42 and SeV-GP31–42, and in the trailer region of SeV-AGP1–55, and their consequences on the promoter-proximal small RNA transcribed from G/Pr and AG/Pr, are also indicated.