Students taking my virology course at the University of Leicester get a weekly newsletter containing extra links relevant to the lectures. This week we have been looking at virus genomes and the class notes are from Principles of Molecular Virology, chapter 3.
Where do new viruses come from?
In this paper the authors use poliovirus as a model of how RNA viruses, a group that includes the common cold, flu, and hepatitis A and C viruses, recombine their genomes. When genomes recombine, novel viruses can result. The authors show that they can predict where polioviruses will recombine and prove their prediction by building a virus that recombines at higher frequency. GC-rich regions of the genome increase recombination frequency significantly.
Identification and Manipulation of the Molecular Determinants Influencing Poliovirus Recombination. (2013) PLoS Pathog 9(2): e1003164. doi:10.1371/journal.ppat.1003164
Virus genomes and genetics
A Roadmap to the Human Virome (2013) PLoS Pathog 9(2): e1003146. doi:10.1371/journal.ppat.1003146
Despite the rapid progress being made toward deciphering the human virome, several roadblocks remain to its full characterization and utilization. This article is an abbreviated list of these problems and possible solutions.
Replication of DNA Virus Genomes
What is the rule of six?
The rule of six describes a requirement for particular viruses to have a genome length with a multiple of six. The viruses that have been proved to prescribe to this rule are the members of the Paramyxoviridae, but, based on simply counting the number of nucleotides within the genome, it could extend to many more viruses within this family and outside it. In order for this process to operate, the virus genome must be enclosed within its protein coat, specifically N proteins. Each N molecule associates with exactly 6 nucleotides, which gets us to the reason as to why these viruses require their genomes to be a multiple of six.
Reverse Transcription and Integration
Popping the cork: mechanisms of phage genome ejection (2013) Nature Reviews Microbiology 11: 194-204 doi:10.1038/nrmicro2988
Sixty years after Hershey and Chase showed that nucleic acid is the major component of phage particles that is ejected into cells, we still do not fully understand how the process occurs. Advances in electron microscopy have revealed the structure of the condensed DNA confined in a phage capsid, and the mechanisms and energetics of packaging a phage genome are beginning to be better understood. Condensing DNA subjects it to high osmotic pressure, which has been suggested to provide the driving force for its ejection during infection. However, forces internal to a phage capsid cannot, alone, cause complete genome ejection into cells. We describe the structure of the DNA inside mature phages and summarize the current models of genome ejection, both in vitro and in vivo.