Viral Genomes PDF

10.1 Size and Structure of Viral Genomes Viral genome size (Figure 10.1) raries dramatically vary ~1000-fold from smallest to largest smallest circovirus: 1.75-kilobase single strand largest Pandoravirus: 2.5-megabase pairs infects some marine amoebae...

10.1 Size and Structure of Viral Genomes Viral genome size (Figure 10.1) raries dramatically vary ~1000-fold from smallest to largest smallest circovirus: 1.75-kilobase single strand largest Pandoravirus: 2.5-megabase pairs infects some marine amoebae larger than some bacteria RNA genomes typically smaller than DNA viruses  Largest - Pandoravirus Parasitic in amoeba in water Their micrometer-sized ovoid particles contain DNA genomes of at least 2.5 and 1.9 megabases which contains around 2500 genes. https://science.sciencemag.org/content/341/6143/281 Amoeba harbors both bacteria and viruses Amoeba is a unicellular organism which has the ability to alter its shape and lives in the environment (e.g., water). Amoebae Amoeba is the host to bacteria pathogenic to human: e.g., Legionella, causing respiratory diseases Legionella https://aem.asm.org/content/71/1/20 Amoeba Proteus https://microscope-microscope.org/pond-water- https://www.pall.com/en/medical/water-filtration/legionella-filtration.html critters-protozoan-guide/sarcodina/amoeba-proteus/ Amoeba video https://www.pond5.com/stock-footage/item/118800196-amoeba-germ- parasite-microscope-cell-microorganism-movie-vin  Smallest - Circovirus Most known is the porcine circoviruses. Single-stranded circular DNA ) Ooalastaen. e genome of ~1700–3800 ntb nt, encoding only three genes. Causing Post-weaning Multisystemic Wasting Syndrome (PMWS) and Porcine Dermatitis and Nephropathy Syndrome (PDNS). Animal vaccine is available. 1. Niras is important fot cnimals we have vaccine tho 2. https://www.sciencedirect.com/topics/immunology-and-microbiology/circovirus https://www.pigprogress.net/Health/Health-Tool/diseases/Porcine-Circovirus-Infection-Post-weaning-Multisystemic-Wasting-Syndrome-PMWS-and-Porcine-Dermatitis-and-Nephropathy-Syndrome-PDNS/ DImportart The Baltimore scheme of viruses By 1975 Nobel laureate (for their discoveries concerning the interaction between tumor viruses and the genetic material of the cell), virologist, David Baltimore. DNA to aNA Based on the genetic materials of the viruses. → ∅ _ 고 pAAakrectly _ ~ = translate foqrotelas Know the excanplel the key Figure 10.2  ∞ The Baltimore scheme: DNA viruses Read remermber ard based on relationship of genome to mRNA, includes seven classes (Figure 10.2) class I: Double-stranded DNA class II: Single-stranded positive- or plus- strand DNA needs replicative form: double-stranded DNA intermediate All but one ssDNA virus are positive-strand viruses. Aeveninh The Baltimore scheme: RNA viruses class IV: ss(+) RNA viruses, genome is mRNA (so it called “+”) class V: ss(–) RNA viruses, RNA replicase makes (+) strand used as mRNA and template for more (–) strand genomes class III: double-stranded RNA, similar replication as class V class VI (Retroviruses): ss(+) RNA viruses replicate through DNA intermediate Reverse transcription copies RNA into DNA, catalyzed by reverse transcriptase. example: human immunodeficiency virus (HIV) class VII: ds DNA that replicates through RNA intermediate example: hepatitis B also uses reverse transcriptase RNA tA make DNA ≈ ising  The Baltimore scheme: host Only certain Baltimore classes infect certain phylogenies. (Figure 10.3a) Class I (dsDNA) are primary prokaryotic viruses. ^ Class IV (ss(+)RNA) are primary eukaryotic viruses. _ fungi only infected by classes III and IV ^ Most class I and class V viruses have animal hosts instead of ? plants. More class II viruses have plant hosts instead of animals. _ Class VI (Retroviruses) infect only animals. _ class VII more common in plants than animals ^ be curions) why ? Next slide ! ( You should  Viral protein synthesis is in sequence Viral protein synthesis early proteins synthesized soon after infection ^ usually enzymes made in small amounts ^ nucleic acid polymerases, proteins that shut down host transcription and translation late proteins synthesized later ^ structural and assembly proteins ^ made in large amounts s eventually, new virions assembled and exit by lysis or budding  Viral Evolution When did viruses appear? Viruses may have arisen after cells. remnants of cells that replicate with the help of a live cell Viruses as part of the “RNA world” may have played a role in transition from RNA to DNA. Viruses may have been first forms of life (precellular). Why did viruses appear? mechanism to quickly move genes  Proteomics support an early not 100 % Figures are logicald but may be accurate appearance of viruses.. Proteomics suggests viruses originated from ancient cells containing segmented RNA genomes that existed before last universal common ancestor (LUCA) of modern cells. ^ (Figure 10.4a) would have been end of “RNA World” Evolutionary pressure eliminated cells, leaving protein shell to protect genome, and forced dependence on hosts for replication functions. RNA viruses seem to be older than DNA viruses, with dsRNA being oldest of all.  Viral phylogeny Universal phylogenetic tree constructed from combination of protein sequences and structural features. RNA viruses precede DNA viruses, lead to three domains of cellular life. Few groups of viruses have trees assembled from sequences of ^ shared/common genes/proteins. example: nucleocytoplasmic large DNA viruses (NCLDV): Mimivirus and relatives (Figure 10.5) Most viral genes from nature have no existing homologs, so ^ much of their genomes will be new to biology. Figure 10.5