Analysis of specific binding involved in genomic packaging of the double-stranded-RNA bacteriophage phi6.

The genomes of bacteriophage phi6 and its relatives are packaged through a mechanism that involves the recognition and translocation of the three different plus-strand transcripts of the segmented double-stranded-RNA genomes into preformed polyhedral structures called procapsids or inner cores. The packaging requires the hydrolysis of nucleoside triphosphates and takes place in the order segment S-segment M, segment L. Packaging is dependent upon unique sequences of about 200 nucleotides near the 5' ends of plus-strand transcripts of the three genomic segments. It appears that P1 is the determinant of the RNA binding sites. Directed mutation of P1 was used to locate regions that are important for genomic packaging. Specific binding of RNA to the exterior of the procapsid was dependent upon ATP, and a region that showed a high level of cross-linking to phage-specific RNA was located. Antibodies to peptide sequences were prepared, and their abilities to bind to the exterior of procapsids were determined. Sites sensitive to trypsin and to factor Xa were determined as well.