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Virology Review 2

Large & Small Nuclear DNA Viruses

Replication is exclusively nuclear Replication of these viruses is very dependent on cellular factors
Examples of Small Nuclear DNA viruses Parvovirus; Papillomavirus; Polyomavirus
Examples of Large Nuclear DNA viruses Adenovirus; Herpesvirus
Replication is dependent on Cellular DdDp & DdRp Replication of Small DNA viruses
Small DNA viruses infect cells... by inducing the cell into S phase (DNA synthesis pahse) OR they must find cells already going through S phase
Polyomavirus & Pappilomavirus infect cells ... these viruses infect cells by inducing them into S phase
Parvovirus infect cells... this virus infects cells that are already going through S phase (can't induce)
Small DNA viruses may integrate their viral genome into the host chromosomes Small DNA viruses may integrate their viral genome into the host chromosomes
Efficiency/Economy with which Small DNA virus genomes are organized the cis-signals for transcription, DNA replication, RNA processing, & translation are concentrated and often overlap
Parvovirus Structure Small Single-Stranded DNA virus, Replicate in Nucleus, Icosahedral Symmetry, Non-Enveloped
Autonomous Parvoviruses This type of Parvovirus only replicates in already dividing cells
Dependovirus This type of virus needs a helper virus
DNA must become ds before transcription DNA must become ds before transcription
Adeno-associated Virus (AAV) A dependovirus. It is an incomplete virus that needs a co-infected cell. Site specific-integration
Parvovirus Genome Structure Genome is flanked by 2 inverted terminal repeats. Contains 2 ORFs, 6 major RNA species, 3 promototers & alternative splicing signals. It has a ss region, the ends are ds (loop)
Parvovirus ORFs: ref & cap repORF encodes regulatory proteins (replication, gene expression, packaging). capORF encodes for structural proteins
Papillomavirus Structure Small, icosahedral capsid, non-enveloped, circular dsDNA that is associated with histones
Papillomavirus genotypes are considered distinct if... if the nt sequence of specific regions of viral genome differ by 10+%
Papillomaviruses infect either _________ or __________ of a person Infect either mucosa or skin
Papillomavirus genome structure 2 transcriptional promoters & 2 polyadenylation signals (early & late) on the same DNA strand
Papillomavirus Early proteins E1-E7 stimulate cell proliferation & enable viral DNA replication
Papillomavirus Late proteins L1 & L2 form the capsid
Papillomavirus: splicing? Splicing generates 10+ different mRNAs
Polyomavirus Features small, icosahedral capsid, non-enveloped, dsDNA associated with histones, lytic & non-lytic cycle
Members of Polyomavirus Family SV40 virus, BK virus, JC virus
Role of Polyomaviruses in research important model used to study basic mechanisms of tumorogenesis in mammals, mammalian RNA synthesis & processing, SNA replication, & signal transduction
Polyomavirus enters the cell via... Endocytosis (bidning to MHC-1)
Polyomavirus uncoating occurs... in the nucleus
Polyomavirus gene organization Organized in 2 divergent transcription subunits, only 1 ORF
Polyomavirus gene expression Early phase Proteins needed for DNA replication; Regulatory proteins (non-structural); Often proteins which alter host cell
Papillomavirus activity in nucleus Genome replication, nucleocapsid formation, & virion maturation
What is the Large T antigen? a large, multifunctional protein that is involved in cellular process like transcriptional activation & repression, differentiation, and stimulation of cell cycle
What does Large T antigen interact with? it interacts with p53 and pRb
What does Small T antigen interact with? it interacts with cellular phophatase, PP2A
Function of large T-antigen in DNA replication Recruit DNA polymerase
Parvovirus Genome Structure, single & double stranded? Single stranded region, with ITR double-stranded ends. The ds loop acts as a primre for DNA synthesis
Polyomavirus, replication occurs when? replication occurs after early gene expression and before late protein expression
Polyomavirus & Host RNA polymerase Host RNApolym is recruited to promoter & makes 1` transcript
Polyomavirus & Alternative Splicing The 1` transcript is alternatively spliced producing (1st) Small T antigen and (2nd) Large T antigen
Polyomavirus & 1 ORF Has 1 ORF that makes 2 products, efficient for small viruses
Large T binds to ______________________ and functions as a ___________________ and recruits DNA polymerase during DNA synthesis. large T binds to an ORIGIN OF REPLICATION and functions as a REPLICATION PROTEIN and recruits DNA polymerase during DNA synthesis.
Large T recognizes a ______________ and functions as a _________________ during Late RNA synthesis. Large T recognizes a PROMOTER and functions as a TRANSCRIPTION FACTOR during Late RNA synthesis.
VP2 and VP3 are made via... made by a 2nd alternative splicing of 1` transcript
VP1 is made via... made by shifting, changing the start of the reading frame in the 1` transcript
Function of Large T antigen besides in DNA rep Increased transcription of late genes; Decreased transcription of early genes; cellular transformation
Function of Large T antigen is pahse progression Amount of Large T may tell the cell to slow down early transcription to move to next pahse, lower affinity binding site
Polyomavirus Assembly & Maturation Occurs in Nucleus simultaneously
Polyomavirus Assembly Capsid proteins in cytoplasm are moved to nucleus where they assemble with viral DNA (histones)
Inclusion Bodies Large number of capsides accumulated in nucleus
Polyomavirus Release Released via Cell Lysis (b/c its non-enveloped)
Polyomavirus - Host cell provides what? DNA synthesis machinery, RNA synthesis machinery, & Histones
Polyomavirus 2 Types of Infection Productive (lytic) infection & Non-productive (abortive) infection
Adenovirus Structure small, non-enveloped, icoasahedral
Adenovirus DNA linear, Double-stranded DNA, genome NOT associated with histones
Adenovirus Cell Entry Fibers bind to cell surface recptors, Endocytosis, Lyse endosomes
Adenovirus Uncoating Occurs in steps near nucleus
Adenovirus Nuclear Entry DNA released into nucleus through nuclear pore
Adenovirus mRNA synthesis: Immediate Early IE-A and IE-B
Adenovirus mRNA synthesis: Early genes scattered
Adenovirus Early mRNA promoter many,not 1 single promotor, clusters, can make things only when needed
Adenovirus early proteins proteins needed for transcription of other early mRNAS (E1a gene product), for DNA synthesis, that alter expression of host genes, that interfere with host anti-viral defenses, and that interfere with cell cycle regulation
Adenovirus: DNA polymerase Encodes for its own DNA polymerase! Does not use the host's.
Adenovirus: DNA replication Displace strand, similar to semi-conservative
Adenovirus: Terminal Protein (TP) Functions as a primer, recruites DNA polymerase ; convalently linked to 5` end of all viral ssDNA strands
Adenovirus: ss Binding protein binds to DNA strands during replication to protect it
Adenovirus: Late mRNAs code for structural proteins, late genes in block
Adenovirus: Primary transcript (only 1 is made) is processed & spliced A LOT to generate various monocistronic mRNAs
Adenovirus: Late transcription Only 1 promoter driving expression of ALL late proteins
Adenovirus: Steps of Processing the Primary transcript Cut at poly(A) site, polyadenylate to add tail, splicing, intron removal
Adenovirus: Assembly & Maturation Occurs in nucleus simultaneously
Adenovirus: Release Cell Lysis
Adenovirus: Host cell provides what? DNA synthesis accesory factors, RNA synthesis & modification enzymes. (does not provide polymerase or packaging proteins!)
Adenovirus: Early mRNA processing processed by host cell capping, methylation, polyadenylation, and splicing enzyme systems
Herpesvirus Structure Icosahedral nucleopcapsid surrounded by tegument & a liped bilayer with peplomers; enveloped. Also contains cellular components.
Peplomers The glycoprotein spikes located on the lipid bilayer of a herpesvirus that are important for attachment
HSV 1 Herpes Simplex Virus Type 1 - cold sores
HSV 2 Herpes Simplex Virus Type 2 - genital
Herpesvirus Type 8 Kaposi's sarcoma
Other Typres of Herpesvirus Varicella zoster virus (chickenpox), Epstein-Barr virus (infectios mono), Burkitt's lymphoma
Herpesvirus: Genome Large, linear, double-stranded DNA
Herpesvirus Attchment & Penetration Fusion with cell membrane, release of genome into cell, leaves footprint on cell membrane
Synctia Formation Footprint has viral attachment proteins so if infected cell gets near uninfected, can bind together and form synctia
Herpesvirus: Immediate Early - alpha-mRNAs stimulated by cellular DNA-dependent RNA-polymerase. a virion protein that interacts with host transcription factor & increases transcription from alpha promoters
Herpesvirus: Alpha proteins are made in the cytoplasm but move back to nucleus act as transcription factors for bet-mRNAs. Also enable beta promoters to be recognized
Herpesvirus: Early - beta-mRNAs encode VIRAL DNA-dependent DNA-polymerase, DNA binding proteins, thymidine kinase, ribonucleotide reductase
Herpesvirus: Beta proteins synthesis results in decrease of alpha-mRNA synhtesis.
Herpesvirus: Beta proteins & Chemo They are virally encoded enzymes, so they are good targets for viral chemotherapy
Herpesvirus: Uncoating Partially uncoaded when enter cell, fully uncaoted when entering nucleus
Herpesvirus: DNA replication Variant form of rolling circle mechanism. DNA may recircularize in cell, viral proteins required. Repetitive sequences at ends of viral genome are involved with circulization and packaging.
Herpesvirus: Late (gamma) gene transcription occurs after DNA replication & outside of nucleus. proteins are then transported INTO the nucleus for packaging
Gamma-proteins mainly structural, one must be packaged in the virus to intiate the first step of alpha-gene transcription
Herpesvirus: Tegument an amorphous proteinaceous substance that surrounds the herpes nucleocapside. It contains 8+ viral proteins
Herpesvirus: 5 glycoproteins that participate in cell entry gB, gC, gD, gH, and gL [B,H, & L are structurally conserved among all herpesviruses & essential to entry)
Herpesvirus: Coreceptors HVEM (herpes virus entrey mediator) and Nectin-1 & nectin-2
Herpesvirus: Virion Host Shutoff Protein (vhs) viral protein that participates with rapid degradtion of cellular mRNAs, causing a shutoff of host protein synthesis
Herpesvirus: VP16 binds to DNA & is an activator of transcription/expression of alpha-genes
Herpesvirus- alpha-genes encode DNA binding proteins that play a role in viral transcription
Herpesvirus- beta-genes encode DNA replication & more transcription factors
Herpesvirus: Assembly in Nucleus capsid assembly occurs in nucleus after gamma-proteins are synthesized. DNA concatemers are cleaved into monmers & packaged as well.
Herpesvirus: Release from Nucleus -> nucleocapsid/tegument bud out of nucleus, budding from ER lumen, cell lysis
Herpesvirus: Notes on Replication - gene blocks No obvious early/late gene blocks
Herpesvirus: Notes on Replication - independence More independent than other small viruses & because more independent, harder to target with drugs
ALPHA Herpesviruses: 2 Types 1. Herpes Simplex Virus (HSV) ``` 2. Varicella Zoster Virus (VZV)
Herpes Simplex Virus: Productive Infection Lytic replication in epithelial cells - Retrograde transport moves capsid up axon - latent HSV episome (NOT-integrated) lies in ganglia
Episomes Circular DNA that replicates independently of the cell's nucleus
Latency Associated Transcripts (LATS) Limited group of viral genes that are expressed during latent stage
Varicella Zoster Virus (VZV): Chickenpox The only herpesvirus that spreads preson to person by coughing or sneezing
Varicella Zoster Virus (VZV): Shingles latent chickenpox becomes reactivated >60yo. Can NOT be spread person to person
BETA Herpesvirus Cytomegalovirus
Cytomegalovirus (CMV) an opportunistic infection of ImComp pple. Causes 21% of Mono cases
GAMMA Herpesvirus Epstein-Barr Virus
Epstein-Barr Virus (EBV) Causes 79% of mono cases; associated with Burkitt's Lymphoma
Acyclovir Most common Rx for Herpesvirus; Guanosine analog, can be used for long-term prophylaxis, action limited to virally-infected cells
Acyclovir Mechanism of Action Converted to ACG-monophasphate by Herpesvirus Thymidine Kinase (TK). 3 phosphates added, 1st by cellular or viral TK, 2nd & 3rd by cellular kinases
WHY DOES HERPES SIMPLEX CODE FOR ITS OWN THYMIDINE KINASE? HSV brings it’s own kinase, so it can increase the pool of phosphorylated nucleosides and can grow in non-dividing cells
What is Thmydine kinase? “Thymidine kinase” is a misnomer
Created by: lbr9349