Viral Subunit Reassortment
Watch the animation on the left side of the screen to see how different viral strains can be generated by a process called subunit reassortment. The animation was adapted from a demonstration developed by HHMI investigator Donald E. Ganem, M.D., for the HHMI's 1999 Holiday Lectures on Science, 2000 and Beyond: Confronting the Microbe Menace.
To view the animation, use the controls at the bottom of the view screen. Expect several pauses as each section of the animation loads and the text in this panel updates to describe the relevant step in the animation.
Part 1: Introduction
Reassortment is the exchange of entire RNA segments, also called subunits, between genetically related viruses. This animation depicts a single human cell infected concurrently with two strains of influenza virus. Once inside the cell the eight RNA subunits of each virus replicate to produce additional RNA subunits. Different combinations of the RNA segments generated from each parental virus are incorporated into progeny viruses. Click on "Play" to start the animation.
The animation begins with a schematic view of a human cell showing the cell membrane, cytoplasm, and nucleus.
Part 3: The viruses
Two different influenza viruses approach the surface of the cell. Virus 1 contains blue genomic RNA subunits, and virus 2 contains red genomic RNA subunits. The RNA subunits are surrounded by a protein shell that resides inside a viral envelope.
Part 4: Infection
The two viruses attach to receptors on the cell surface. The membrane of each virus fuses with the cell membrane, and the viral genome, surrounded by the protein shell, is released into the cell cytoplasm.
The protein shell of each virus disassembles in the cell cytoplasm, and the RNA subunits enter the cell nucleus.
Part 6: RNA replication
The RNA subunits replicate to produce many identical copies. The newly synthesized RNA subunits from each parental virus mix freely in the cell nucleus.
Different combinations of RNA subunits originating from the two parental viruses are assembled with newly made proteins into viral particles. As a result, a variety of new virus types are produced from the infected cell.
Part 8: Conclusion
The animation ends with a close-up view of the progeny viruses. Some progeny viruses are identical to the parental viruses (shown as containing RNA subunits of only one color), while others are sometimes dramatically different.
Viral Subunit Reassortment Background
Unlike bacteria, viruses are acellular (not cellular). A virus particle contains only one type of nucleic acid, either RNA or DNA, which is sometimes surrounded by a protein coat. Sometimes the coat is further encased in a membrane called an envelope. Viruses can only reproduce by using the cellular machinery of other organisms. Viruses acquire new traits through mutation and reassortment (the process described in this animation) of their genetic material.