RNA-BINDING, PACKAGING AND POLYMERASE ACTIVITIES OF THE DIFFERENT INCOMPLETE POLYMERASE COMPLEX PARTICLES OF DSRNA BACTERIOPHAGE-PHI-6

phi 6 is an enveloped dsRNA bacterial virus. Its segmented genome resi des inside the virion associated polymerase complex which is formed by four proteins (P1, P2, P4 and P7) encoded by the viral L segment. Com plete and incomplete polymerase complex particles can be produced usin g cDNA copies of this largest genome segment. We have analysed the cap acity of the different purified particles to (1) package phi 6 (+) sen se genomic precursors and unspecific RNA, (2) synthesize (-) and (+) s trands and (3) bind phi 6 specific and unspecific RNAs. Both (-) and ( +) strand synthesis polymerase activities were found to be associated with protein P2. In addition to complete particles, particles lacking protein P2 were found to package and protect genomic precursor ssRNAs. Protein P7 was needed for efficient packaging. Regulation and specifi city of the packaging were found to be independent of P2. Particles co mposed of proteins P1 and P4 did not package or protect RNA but did bi nd phi 6 genomic (+) strand RNAs. The three phi 6 (+) strands bound in equal amounts to the particles when tested alone in a filter binding assay. In competition experiments they competed each other for binding , indicating that individual binding sites for the three genomic (+) s trands do not exist. Differences in RNA binding competition among the four particles were observed, suggesting that packaging specificity is achieved by complex interactions of proteins and genomic (+) strand R NAs during the advancement of the packaging process after the initial binding events.