Week 8 -- Monday and Wednesday Notes
Week 8 -- Monday and Wednesday Notes BIOL 123 001
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BIOL 123 001
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This 6 page Class Notes was uploaded by Anastassia Erudaitius on Monday May 23, 2016. The Class Notes belongs to BIOL 123 001 at University of California Riverside taught by Dr. Rao in Spring 2016. Since its upload, it has received 12 views. For similar materials see Virology in Biology at University of California Riverside.
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Date Created: 05/23/16
Virology Lecture 5/16/16 In poliovirus the genome is only one RNA Influenza virus the genome is 8 RNA o Only known example in human and animals of multiple genomes in a virus In plant viruses there is a wide range of virus genome types and capsid types o Helical symmetry/ rod-shaped o Icosahedral symmetry TMV -- Only one virus particle needed to infect a host (only one long rod) Two-component viruses o Two RNAs encapsid separately helical symmetry o Furovirus o Tobraviruses —long and short rod o Need both long and short rods to infect o In all these cases you need both size virions (long and short rod) to initiate infection Three or four component viruses o Hodeiviruses differently sized rods – when you run on a gradient they will separate by size o You need all three rods (or 4) to initiate infection in host Two-component viruses o Each packages different sized RNAs o Size-wise they are similar, look identical but they package different sized RNAs you can separate them on a gradient though because the weight of each will be different since they package different sized genomes Three-component viruses Bromo/cucumoviruses o All icosahedral, identical size o Genome is distributed into 3 different particles o Because the weight of the identical capsids was different, the researches realized that the genomes packages in each must be of varying weight o First virus that showed how these virus genomes are distributed Four component viruses o Alfalfa 4 differently sized virions need all 4 to be infectious o Tobacco streak icosahedrals of different size Five component viruses o 5 genomes o Not much is known about these Brome Mosaic Virus o Very well studied family – Bromoviridae o First isolated from brome grass o Not an economically important viruses but occasionally you do get epidemics caused by the virus in wheat or oat o Because of its genome nature it can replicate to very high levels o RNA virus o Used as a model to study recombination o First virus used to make cDNA o RNA 1 in one particle, RNA 2 in one particle, and RNA 3 and 4 together in one particle o Bromoviruses transmitted by beatles o In order to initiate infection you need all 3 RNAs o Everything is encoded in 3 RNAs o RNA 3 has two genes Encodes movement protein and capsid protein THE CODING PROTEIN IS NOT TRANSLATED FROM RNA 3 RNA 3 produces RNA 4 that encodes for the coding protein RNA 4 is complementary to coding protein region on RNA 3, but RNA 4 is the one that gets translated to make the coding protein The advantage is that the virus can control when the genes get expressed o All RNAs are messenger sense (3’ cap and 5’tRNA like structure) Instead of a 5’polyA tail, they have a t-RNA region (not involved in translatioin) they function as a (-) strand promoter Don’t need to know this in detail o RNA 1 makes 1a protein o RNA 2 makes 2a protein o Life Cycle Enters host by insects RNA gets translated Proteins are produced in ER Virus modifies ER Movement protein moves protein from cell to cell Capsid proteins encases virions Insects pick up the virus and transmit to other plants In TMV everything is encoded in one RNA, so you only need one RNA to infect Methods for studying virus replication o Plants used because they are the natural host o Viral reporter systems o Protoplasts – single cells from the plant, digest the cell wall and leave the protoplasts and can isolate the protoplasts and study viral infection easily o Yeast – good model because so many mutants you can use that are defective in certain functions you can study BMV replication o Messenger sense RNAs – translated directly o Replicase recognizes 3’ end and copies a (-) strand o Then the replicase recognizes the (-) strand and makes a (+) strand o Movement protein is translated from the genomic RNA 3 o Gap between MP and CP used as promoter region o RNA 4 is made from (-) 3 strand not (+)! o Every gene is expressed at a different time, replicase proteins made at very low concentration, capsid protein made at highest concentration o RNA virus, no nucleus involved Packaging scheme for BMV and CMV o All viral genomes ae packaged into different particles o RNA 4 is NOT required in order for infection to occur because it is generated from RNA 3 o Packages RNA 4 in order to make the capsid and virion more stable In influenza all 8 RNAs are packaged into ONE particle and you need all 8 in order for influenza to be infectious Alfamovirus o Makes 4 RNAs like BMV Same replication mechanism o However, this one requires capsid protein in order to initiate infection (BMV does not need this!), RNA 4 is required! (because RNA 4 is translated to produced capsid protein) o Most unusual property of this virus – the nucleic acid AND the protein is required to be infectious o AMV is worldwide o Typical mosaic symptoms o Plant growth stunted, yield decreases o AMV transmitted by aphids o Infects peppers also (often alfalfa and peppers are grown side by side) Potatoes grown at high populations because aphids are not present at high altitudes – can limit infections Advantages o Having multiple components – Each gene can be efficiently manipulated whenever it is needed o Recombinants can develop Disadvantages o Need all three particles to infect host o If you just have RNA 1 and RNA 2 transmitted then the virus cannot move because RNA 3 encodes movement protein **”Will definitely have questions on advantages and disadvantages”** Virology Lecture 5/18/16 Independent – can replicate by themselves Satellite virus ALWAYS encode capsid protein, but satellite RNA does not encode proteins o Satellite RNA require helper virus but they do not encode any proteins Satellite – cannot replicate by themselves, are dependent on a helper virus o Requires another virus to replicate Most satellite viruses associated with plants Satellites o Sat. RNA and viruses are very common as plant viruses o Hijack the viral replicase and use it for their own replication, as a result the helper virus replication decreases o Genomes are extremely small compared to helper viruses (no more than 300 nucleotides) Satellite viruses o Make their own capsid proteins o Dependent on helper virus for replication as well as vector transmission o Slightly larger than satellite RNAs TMV is a very stable virus Satellite RNAs have no sequence homology Final on Thursday, June 9 o Cumulative o 2 more lectures after today o Will get questions from video
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