16.7
ウイルスの突然変異
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Q1: Why do RNA viruses mutate faster than DNA viruses?
RNA polymerase lacks proofreading capability, making it prone to errors during genome replication. DNA polymerase, by contrast, can proofread its work. This difference means RNA-based viruses like HIV accumulate mutations at higher rates, enabling rapid evolution and adaptation to environmental pressures.
Q2: How does reverse transcriptase contribute to HIV's rapid evolution?
Reverse transcriptase, the enzyme HIV uses to replicate its RNA genome, does not proofread. This lack of proofreading leads to spontaneous errors during replication, generating mutations at high frequency. These mutations provide the raw material for adaptive evolution, making HIV difficult to combat with antiviral drugs.
Q3: What role do mutations play in viral drug resistance?
Mutations provide the genetic variation that allows viruses to evolve resistance to antiviral drugs. RNA-based viruses accumulate mutations rapidly due to polymerase errors, enabling them to quickly adapt and survive drug treatment. This process is particularly problematic for retroviruses like HIV.
Q4: How can genome sequencing reveal the origins of emerging viral strains?
By comparing mutations in viral genomes isolated from different hosts and species, researchers can reconstruct evolutionary history and trace viral origins. For example, H7N9 avian influenza analysis revealed the strain likely originated in Chinese domestic duck populations before spreading to chickens and humans through live poultry markets.
Q5: What is a mutation in the context of viral genetics?
A mutation is a permanent change in the sequence of bases in DNA or RNA within a genome. Viral mutations often occur during genome replication when polymerase enzymes make errors. These changes accumulate over time, driving genetic variation and enabling viral evolution.
Q6: How did researchers use mutation analysis to identify the source of H7N9 infections?
Researchers compared mutations in H7N9 viruses from infected humans and various bird species to trace the strain's evolutionary path. The ancestral strain originated in domestic ducks, then underwent recombination reassortment and emergence of new viruses before infecting humans. This work identified live poultry markets as the likely transmission source.
Q7: Why is rapid viral evolution important for epidemiologists during disease outbreaks?
Understanding how viruses evolve through mutation analysis helps epidemiologists track disease origins, predict transmission patterns, and identify outbreak sources. Rapid genome sequencing now makes it possible to investigate viral evolution in real time during epidemics, enabling faster public health responses and outbreak control strategies.