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A virus's polymerase enzymes are often much more efficient at making DNA and RNA than the equivalent enzymes of the host cells, [31] but viral RNA polymerase enzymes are error-prone, causing RNA viruses to mutate and form new strains. [32] In some species of RNA virus, the genes are not on a continuous molecule of RNA, but are separated.
The tumor virus can introduce and express a "transforming" gene either through the integration of DNA or RNA into the host genome. The tumor virus can alter expression on preexisting genes of the host. One or both of these mechanisms can occur in the same host cell.
Viral evolution is a subfield of evolutionary biology and virology that is specifically concerned with the evolution of viruses. [1] [2] Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates (on the order of one point mutation or more per genome per round of replication).
Viruses may undergo two types of life cycles: the lytic cycle and the lysogenic cycle. In the lytic cycle, the virus introduces its genome into a host cell and initiates replication by hijacking the host's cellular machinery to make new copies of the virus. [12] In the lysogenic life cycle, the viral genome is incorporated into the host genome.
The integrity of the DNA was maintained by a group of repair enzymes including DNA topoisomerase. [20] If the genetic code was based on dual-stranded DNA, it was expressed by copying the information to single-stranded RNA. The RNA was produced by a DNA-dependent RNA polymerase using nucleotides similar to those of DNA. [15]
Although somewhat of a misconception, it is not the actual virus that is synthesised, but rather its DNA genome (in case of a DNA virus), or a cDNA copy of its genome (in case of RNA viruses). For many virus families the naked synthetic DNA or RNA (once enzymatically converted back from the synthetic cDNA) is infectious when introduced into a cell.
Viral vectors are routinely used in a basic research setting and can introduce genes encoding, for instance, complementary DNA, short hairpin RNA, or CRISPR/Cas9 systems for gene editing. [8] Viral vectors are employed for cellular reprogramming, like inducing pluripotent stem cells or differentiating adult somatic cells into different cell ...
The first man-made infectious viruses generated without any natural template were of the polio virus and the φX174 bacteriophage. [4] With synthetic live viruses, it is not whole viruses that are synthesized but rather their genome at first, both in the case of DNA and RNA viruses. For many viruses, viral RNA is infectious when introduced into ...