Related Experiment Video
Updated: Aug 23, 2026

Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification
Published on: November 16, 2016
Packaging motor from double-stranded RNA bacteriophage phi12 acts as an obligatory passive conduit during
Denis E Kainov1, Jirí Lísal, Dennis H Bamford
1Institute of Biotechnology and Faculty of Biological Science, Viikki Biocenter, University of Helsinki, PO Box 65, Viikinkaari 1, Helsinki FIN-00014, Finland.
Abstract:
Double-stranded RNA viruses sequester their genomes within a protein shell, called the polymerase complex. Translocation of ssRNA into (packaging) and out (transcription) of the polymerase complex are essential steps in the life cycle of the dsRNA bacteriophages of the Cystoviridae family (phi6-phi14). Both processes require a viral molecular motor P4, an NTPase, which bears structural and functional similarities to hexameric helicases. In effect, switching between the packaging and the transcription mode requires the translocation direction of the P4 motor to reverse. However, the mechanism of the reversal remains elusive. Here we characterize the P4 protein from bacteriophage phi12 and exploit its purine nucleotide specificity to delineate P4 role in transcription. The results indicate that while P4 actively translocates RNA during packaging it acts as a passive conduit for RNA export. The directionality switching is accomplished via the regulation of P4 NTPase activity within the polymerase core.
Related Concept Videos
DNA Bacteriophages
Lytic Cycle of Bacteriophages
Bacterial RNA Polymerase
In most genes, the transcription site is a single base present upstream of the coding sequence. Though RNAP is a catalytically efficient enzyme, it does not recognize...
Bacterial RNA Polymerase
In most genes, the transcription site is a single base present upstream of the coding sequence. Though RNAP is a catalytically efficient enzyme, it does not recognize...
Bacterial Transcription
Transcription can be divided into three main stages, each involving distinct DNA sequences to guide the polymerase. These are:
Lysogenic Cycle of Bacteriophages

