INVITRO REPLICATION, PACKAGING, AND TRANSCRIPTION OF THE SEGMENTED DOUBLE-STRANDED-RNA GENOME OF BACTERIOPHAGE PHI-6 - STUDIES WITH PROCAPSIDS ASSEMBLED FROM PLASMID-ENCODED PROTEINS

The genome of the lipid-containing bacteriophage φ6 contains three segments of double-stranded RNA (dsRNA). We prepared cDNA copies of the viral genoma and cloned this material in plasmids that replicate in Escherichia coli and Pseudomonas phaseolicola, the natural host of φ6. These plasmids direct the formation of viral proteins and the assembly of structures similar to viral procapsids containing proetins P1, P2, P4, and P7. We found that these particles are capable of taking up viral single-stranded RNA and synthesizing the minus strands to produce dsRNA structures. Once the dsRNA is formed, it is then used as a template for the production of viral plus strands in a reaction that resembles normal transcription. The particles were also capable of directly transcribing exogenous dsRNA. The replicase reactions were specific for φ6 RNA, were specific for procapsids, and resulted in substantial incorporation of product dsRNA into particles. These results offer strong support to a model in which genomic packaging is done by performed procapsids.