Bacillus virus phi29

In 1965, American microbiologist Dr. Bernard Reilly discovered the φ29 phage in Dr. John Spizizen's lab at the University of Minnesota. Due to its small size and complex morphology, it has become an ideal model for the study of many processes in molecular biology, such as morphogenesis, viral DNA packaging, viral replication, and transcription. == Structure ==

The structure of φ29 is composed of seven main proteins: the terminal protein (p3), the head or capsid protein (p8), the head or capsid fiber protein (p8.5), the distal tail knob (p9), the portal or connector protein (p10), the tail tube or lower collar proteins (p11), and the tail fibers or appendage proteins (p12*). The main difference between φ29's structure and that of other phages is its use of pRNA in its DNA packaging motor. The φ29 packaging motor is able to generate approximately 57 piconewtons (pN) of force, making it one of the most powerful biomotors studied to date. Early studies such as Anderson (1990) and Trottier (1998) hypothesized that pRNA formed intermolecular hexamers, but these studies had a solely genetic basis rather than a microscopy based approach. In the year 2000, a study by Simpson et al. employed cryo-electron microscopy to determine that, in vivo, only a pentamer or smaller polymer could spatially fit in the virus. This discovery aligned with what was known about the structural geometry and necessary flexibility of the packaging motor's three-way junction. Specifically, the functional domains of pRNA bind to the gp16 packaging enzyme and the structural connector molecule to aid in the translocation of DNA through the prohead channel. == Genome and replication ==

The φ29 phage has a linear dsDNA genome consisting of 19,285 bases. Both 5’ ends of the genome are capped with a covalently bonded terminal protein (p3) that complexes with DNA polymerase during replication. φ29 is one of many phages with a DNA polymerase that has a different structure and function compared to standard DNA polymerases in other organisms. This allows the initiation of DNA replication to be more accurate by having the polymerase complex check a specific sequence before beginning the elongation process. == Applications ==

Nanoparticle assembly Versatility in RNA structure and function provides the ability to assemble nanoparticles for nanomedicinal therapeutics. The pRNA in bacteriophage φ29 can use its three-way junction in order to self-assemble into nanoparticles. This is primarily because RNA nanotechnology is still an emerging field that lacks industrial application and manufacturing optimization of small RNAs. Drug delivery φ29’s DNA packaging system, using pRNA, incorporates a motor for the delivery of therapeutic molecules like ribozymes and aptamers. Triple-negative breast cancer treatment Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer that accounts for ten to fifteen percent of all breast cancer cases. Chemotherapy is the only viable current treatment for TNBC because the loss of target receptors inherent to the disease causes cancer cells to resist therapeutic pharmaceuticals. The three-way junction in the φ29 DNA packaging motor can help sensitize TNBC cells to chemotherapy using a siRNA drug delivery mechanism to inhibit TNBC growth and volume. This treatment can also be combined with anti-cancer drugs like Doxorubicin to enhance therapeutic effects. == See also ==