FIG. 9.

Schematic diagram illustrating a current model of FHV RNA packaging by capsid protein synthesized from either replicating RNA2 or nonreplicating RNA2. The top left quarter (shaded grey) of this stylized cell shows replication of FHV RNA1 and RNA2 (undulating blue and red lines, respectively) on the outer surface of mitochondria (M). The site of RNA replication was identified by Miller et al. (18). The resulting RNA progeny is translated in close proximity to the mitochondria leading to production of coat protein (red dots) and protein A (blue dots) in the vicinity of the viral RNAs. Coat protein has a high affinity for nucleic acids and rapidly packages the viral RNAs into particles. As shown at the right near the bottom, the transcription of baculovirus genomes containing the cDNA of RNA2 (or RNA1; not shown) in the nucleus (N) leads to synthesis of primary transcripts (with asterisk) that are translated shortly after exiting the nucleus. Absence of significant levels of RNA1 or RNA2 leads to packaging of mostly cellular RNA (in green) and only small amounts of primary RNA2 (or RNA1) transcripts. In cases in which cells are infected with baculoviruses that produce FHV RNA polymerase and yield replication competent RNA1 and RNA2, the mitochondrial replication and packaging environment is set up in parallel, leading to two separate populations of progeny virions.