Where do viruses come from and why do they do what they do?
John M. Coffin Tufts University
Tufts University Where did viruses come from? (Actually, I haven’t a clue.)
RNA world
“RNA cell”
Prokaryotes
Eukaryotes Proto cell Why do they do what they do? (Because they can.)
1. However they arose, they have evolved multiple times into a variety of niches. 2. 2 Phases – virion and intracellular. 3. Rely on cell for most or all replicative functions. 4. Virion allows cell-cell and host-host transmission. 5. Their “job” is to direct cells to make more of themselves, not to cause disease (unless it promotes transmission). 6. Long term host-virus co evolution often leads to a well- adapted, relatively benign interaction. 7. Unlike most other viruses, retroviruses have left behind a fossil record that lets us study this evolution. The Retrovirus Replication Cycle
Entry via fusion
Adsorbtion to specific receptor (CD4)
Maturation via protease The Retrovirus Family Tree
Virus Genus HFV Spumaretrovirinae b e l1 , b e l2 MLV Gammaretrovirus FeLV HERV-C WDSV Epsilonretrovirus o rf A , o rf B , o rf C HIV-1 t a t , re v HIV-2 Lentivirus EIAV VMV d u t MPMV s a g n e w e n v MMTV Betaretrovirus HERV-K IAP ASLV Alpharetrovirus
BLV HTLV-1 Deltaretrovirus t a x , re x HTLV-2
New Genes