Fig. 1.

Schematic representation of different mechanisms for subgenomic RNA synthesis. (A) Internal initiation model (Miller and Koev, 2000), (B) Premature termination model showing termination either during (−) and (+)-strand synthesis (White, 2002), (C) Leader-primed transcription model, (D) Discontinuous template synthesis (Pasternak et al., 2006). Genomic and SG RNA (+)-strands are depicted as horizontal yellow boxes, the (−)-strands are depicted as green boxes, the ovals represent RdRp enzymes capable of starting/stopping at the internal initiation SGP promoters that are depicted as blue SGP boxes. The leader TRS (L-TRS) and the body TRS (B-TRS) are represented by dark green and brown boxes, respectively. Refer to the text for details.