Genomic RNA Packaging and Replication in the Cystoviridae
from: Segmented Double-stranded RNA Viruses: Structure and Molecular Biology (Edited by: John T. Patton). Caister Academic Press, U.K. (2008)
The Cystoviridae, bacteriophages with genomes of 3 dsRNA segments, produce empty procapsid structures that are capable of packaging transcripts of their genomic segments, synthesizing minus strands to form dsRNA and finally transcribing the genome and secreting the plus strands from the complex. All of these reactions can be carried out in vitro using particles assembled from proteins whose synthesis is directed by cDNA copies of the viral genomes and RNA transcribed from cDNA copies of the genomic segments. Packaging is dependent upon the specific binding of pac sequences near the 5' ends of the transcripts to sites on the outside of the procapsids. Packaging is serially dependent in that the transcript of S is packaged first and then that of M and finally the transcript of the L segment. The in vitro packaging and replication system has facilitated studies of the rules of packaging, replication and recombination in this virus family. It has also led to the development of powerful reverse genetics technology resulting in the effective manipulation of the structure and content of the viral genomes read more ...