INTERFERENCE WITH BACTERIOPHAGE-PHI-6 GENOMIC RNA PACKAGING BY HAIRPIN STRUCTURES

Bacteriophage phi 6 has a genome of three segments of double-stranded RNA enclosed in a procapsid composed of four different proteins. The p reformed procapsid is capable of packaging plus-strand transcripts of the genomic segments in an in vitro reaction. Minds-strand synthesis w ithin the procapsid then results in the production of the double-stran ded RNA genome. When plus-Strand transcripts contain strong hairpin st ructures near the 3' ends, they are subject to heterologous recombinat ion to remove the hairpins. We now find that the sequences bounded by the hairpins as well as those 3' to them are excluded from particles i n packaging reactions. This finding implies that packaging occurs from the 5' end and that the explanation for the faicilitation of recombin ation by the hairpin structures is the lack of entry of the 3' ends ra ther than a difficulty of progressing through the hairpin by the phage polymerase. Packaging bf segment M is dependent on the packaging of s egment S. An S segment containing a strong hairpin is able to facilita te the packaging of segment M. This result implies that there is more than one entry pore into the procapsid.