Lecture 5 Flashcards
What are the two types of cycle used by bacteriophage?
Lytic cycle - Phage replicates and causes cell lysis to escape
Lysogenic cycle - Phage integrated its DNA into bacteria. DNA can be passed onto daughter cells. During stress phage will replicate and cause lysis to leave
Outline the actions of the T4 lysis proteins
Holin T accumulates and forms a multimer at correct time in inner membrane
Endolysin will pass through the Holin T multimer and degrade the peptidoglycan
SPANINS can then diffuse freely to outer membrane and inner membrane and lead to lysis
How is lysis controlled during the lysogenic cycle?
Antiholin stops holin multimerising
Outline phi 6 lysis
- P8 attaches to prohead of nucleocapsid
- P3 spike protein assembled in the membrane via P6
- P9 and P12 induce vesicularisation of the membrane around the nucleocapsid
- Lysin P5 and membrane protein P10 cause lysis
Name a phage which can exit a cell without causing lysis
Outline its action to exit
M13
- Prophage of twisted single stranded closed cicular DNA coated with gp5
- Gp5interacts with gp1 in membrane which triggers opening of extrusion channel, through gp4
- gp5 swapped for gp8 and gp3, 6, 7, 9 added to ends of the phage (all from inner membrane of the bacteria)
- Mature phage is released
What is commonly used by animal virus for lysis?
Viroporins - encoded by late virus genes and form pores in the membrane
What stratergy is used by baculoviridae?
Why?
Occulusion body - polyhedrin coat around more than one capsid
Infects anthropods and crustaceans, and hence are more resistant to environment and can infect via ingestion
How do enveloped animal viruses exit the cell?
Budding
Where does the envelope around enveloped animal virus come from?
The membrane of the cell
Why do different viruses have different sites of budding?
Different requirements for the enveloped fulfilled by different membrane types
Where in the cell can viruses bud from?
- Plasma membrane - retroviruses, filoviruses
- Golgi - Herpesvirus, poxvirus
- Nucleus - used to travel through ER for golgi or ER membrane envelopes
- ER -HCV
- Mitochondria - HCV
How is budding both push and pull?
- Viral membrane glycoprotein assembly in outer membrane pulls membrane out
- Innner viral proteins and nucleocapsid pushes membrane out
Ouline influenza virus budding
- HA and NA cluster in lipid rafts
- M1 binds to cytoplasmic tails of HA and NA and acts as binding site for vRNP’s
- Polymerization of M1 causes elongation
- M2 is recruited and causes scission at the bottom of envelope
How is M2 hypothesised to work?
M2, a viroporin, is targeted to viral budding sites by binding cholesterol
Acting as a proton channel the M2 reduces the electrical repulsion between opposing monolayers of the membrane to allow budding
What is required to allow budding through different membranes?
Different viroporins
What is the viroplasm?
An electron dense cytoplasmic rich inclusion formed by large DNA viruses and dsRNA viruses
What are spherules?
50-400nm membrane invaginations found in several different membrane bound organelles
What are double membrane vesicles?
Membraneous structures derived from ER or golgi having a diameter of 200-300nm
What are nuclear virl factories?
Sub nuclear compartments formed by some viruses for replication
e. g. Herpes simplex - the replication compartment
e. g. Baculoviruses - virogenic stroma
What is the difference between HBV and HCV?
Both cause liver damage but HBV cuases liver disease and cancer whereas HCV causes liver transplant
HCV can’t be detected as well and is a lipoviroparticle
What is HCV dependent on for production?
Hepatic very-low density lipoproteins
What does HCV use for attachment?
What is required for its internalisation?
Heparin sulphate
The LDL receptor
Where does the viral replication complex of HCV form?
What is essential for this formation?
The ER
A poly protein of structural and non-structural proteins inserted into the membrane which curves the membrane and acts as scaffold for RC assembly
Why does HCV infect liver cells?
The RC is located next to wher lipid doplets are being formed to encapsulated the capsid in the droplet and have glycoproteins on the outside
These lipid droplets are formed in liver cells
Why does HCV need to exit via the golgi?
To mature into an infectious particle
Where does HIV assemble its capsid?
At the site of Budding
Oultine HIV budding
- gp120 and gp41 produced and inserted into membrane
- Gag interacts with these proteins to start budding
- Gag interacts with cellular ESCRT machinery
- Ap2 restricts Gag to membrane and interaction between Ap1 and ESCRT causes budding
- A coat of clathiring is also incorporated under the envelope
- Tetherin hold the viral particle on the cell membrane in an attempt to alert the immune system
- Ap2 and clathirin then removes tetherin
How id HIV matured?
Viral protease cleaves Gag and Gag-Pol to form mature proteins
