Mutations Educational Materials

Mutations Mutations are one of caused the common causes errors of genetic variations in viruses. Onereplication. cause is nucleotide substitution by polymerase in reading the template during Mutations can be beneficial, detrimental, or have no effect on the organism. Below are several factors that can cause mutations in viruses: 1.forms Errors in the polymerase that the replicates the genome due toontherough incorporation of tautomer in nucleotide bases during replication process. Based calculations, the virus mutation rate roughly ranges between 10-8 and 10-4 substitutions per nucleotide per cell infection. DNA viruses are in the range of 10-8 and 10-6 while RNA viruses are in the range of 106proofreading and 10-4. The polymerases of most RNA viruses (except coronaviruses) do not have activity (RT) 3′exonucleases and are 3′exonucleas. therefore moreDNAerror-prone than DNA viruses. Reverse transcriptase also has no activity viruses are more molecularly stable haveerror mutationbecause rate of they RNA viruses to becorrection higher thanmechanism DNA viruses.during replication. This causes the 2.9.1b). The This size ofis the viral togenome is negatively correlated with the rate ofvirus viraland mutation (Figure thought be related to the interaction between the DNA Damage Response (DDR). DDR is a signaling process carried outinterference, by the host apoptosis, to respondtranscription if there is DNA damage, with cell responses in the form of cell cycle or DNA repair. Polyoma viruses, papilloma viruses, and parvoviruses induce and depend on the DDR signaling pathway for efficient replication. Theserely viruses have small circular DNAreplication genomes that do not code for polymerase. As such, they directly on the cellular machinery, in contrast to larger DNA viruses.which It is offers possible that some small viruses promote DDR to prolong the S phase of the cell cycle, a better environment for replication. DDR consistsofofthisanpolymerase error-pronein viral DNAreplication polymerasecanforleadre-synthesis of cut strands, involvement to higher mutation rates. and the 3.Apolipoprotein RNA virus mutations are strongly influenced by factors encoded by other hosts. For example, B mRNA-editing catalytic polypeptide-like enzyme (APOBEC) is a protein family ofA study cellularproves cytidinie deaminase that functions as an innate cellular defense against retroviruses. thaterror mutations APOBEC can enzyme. increase the HIV-1 mutation rate by ≥40-fold above the rate ofproduced the ReversebyTranscriptase 4.nitric Chemical compounds canandinduce mutations. Several agents can cause mutations such asin acid (alkaline effect) materials such as UV light and X-Ray. Some RNA viruses nature have not found to have manybyvariants. This does notbeneficial mean the mutation rateinisterms slow. Itofistransmission possible thatbeen the mutation produced the RNA virus is not for the virus and replication, the wild-type version of the virus.causing the virus mutant to fail to adapt in nature compared to 7.3.2 Examples of Phenotypic Changes in Mutant Viruses Phenotype is a characteristic that isoriginating visible andfrom can abeseries seen.ofThe phenotype is steps the result ofona functional protein being expressed, protein synthesis based awilltemplate from the geneticofmaterial. Changes in the composition of genetic material in mutants change the phenotype an individual.Examples of phenotypic changes in mutant viruses include. 1. Sensitive to temperature 2. Change of host 3. Resistance to drugs 4. Deficiency of certain enzymes 5. Can live at high temperatures 6. Can cause different symptoms to the wild type 7.3.3 Recombination Recombination is orthemore formation of parent a newgenomes. genome through the covalent bonding ofDNA genetic material from two different Recombination occurs with both andof RNA viruses, often with the participation of the viral replication machinery. Various types viral recombination areatrecognized based on the structure ofstrands, the crossover site. Homologous recombination occurs the same site on both parental while non-homologous recombination occurs atasdifferent sites of the geneticoccurs fragments involved. A particulargenomes, type of recombination, known shuffling or reassortment, in viruses with segmented which can swap complete genome segments, resulting ininnew combinations ofoccur segments. This nonrecombination is relatively rare in RNA viruses, but DNA viruses it can at a much higher frequency than homologous recombination. Among RNA the viruses, recombination is very frequent in Retroviruses (ssRNA-RT), especially in HIV, where rate of recombination per nucleotide exceeds mutation.