4 Bacteriophage 2 Flashcards
What is Tectiviridae
PRD1
What is the structure of PRD1
Linear ds DNA with protein (P8) bound to each end
What capsid does PRD1 have
Icosahedral
What are the membranes of PRD1 like
Internal membrane within capsid
What binds to host in PRD1
Any spike can act as a receptor to bind to host
what does PRD1 host range/receptor infect
Any gram-negative cell that contains the broad host-range plasmid - RP4
Where does PRD1 bind
Phage does not bind to pills instead binds to DNA transfer apparatus
How is DNA transfer mediated by the membrane
Outer membrane penetration requires proteins
Membrane containing P11 forms tube
Delivers enzyme to make hole in PG (P7)
Fusion with cell membrane results in DNA transfer
What occurs in PRD1 infection
Receptor recognition (P2) irreversible binding
Outer membrane penetration (P11)
PG digestion (P7) deliver P7 enzyme through outer membrane - fusion of lipids in tube and mechanisms
DNA translocation
How are PRD1 core subunits
Translation in cytoplasm
Before release from ribosome start to form core trimers
First part of protein spontaneously forms trainers
When released from ribosome have unstructured tails - wait till virus made high enough concentration
As they pack, form coiled interface structures - line up form hexon structures
PRD1 replication cycle
- Proteins self assemble, form capsid subunits
- Structural membrane proteins located in cell membrane of host
- Vision assembly at host membrane
- Host membrane with vision proteins engulfed during formation of capsid shells
- DNA packaged by P9 ATPase
How does phage MS2 replicate
Positive strand RNA enters cell
1. Directly translated to make early phage proteins for DNA replication
2. Also used to synthesise negative strand RNA from positive stand template
Translated to make more vital structural proteins
Positive strand packaged into capsid shells
Lysis protein translated from positive strand
What is negative strand RNA used for
Used as template to make more copies of positive strand
What is an example of dsRNA phage
Cystoviridae
What is cystoviridae in eukaryotes
Reovirus
What can be seen through a microscope when looking at a cystoviridae
Lipid
What is cystoviridae related to
Closely related to reoviridae
What is reoviridae
Rotavirus that infects humans
What does cystoviridae infect
Infects plant pathogenic bacterium Pseudomonas syringe
Binds to host cell via type IV pilus
Retractable ‘twitching’ pili
What is the structure of cystoviridae
Genome with 3 dsRNA genome fragments
Packaged into pro capsid core
Procapsid covered by protein shell
What is on the procapsid shell of cystoviridae
Lipid containing molecule
How does cystoviridae infect
- Bind to type IV pilus
- Fusion of P6/P3 with outer membrane
- Cell wall degraded
- Filled procapsid crosses inner membrane
- Filled procapsid RNA polymerase copies genome, RNA polymerase reading inside and makes molecules on outside
- mRNA makes new procapsid proteins
- Replication stops when new P8 protein shell made around filled procapsid
- Membrane proteins inserted into inner membrane form phage envelope
How are cystoviridae packaged
Part of procapsid has specific binding site for small RNA molecule
Nucleus acid guided into procapsid shell - negative charge of nucleic acid repel proteins so they reorganise and form a new shape
Specific binding site on shell form - directed into shell
Form fully structured shell with a segment of each
Phage P1
Myoviridae
What are the myoviridae ends like
Ends of linear genome are identical
What is terminal redundancy
Copies of terminal genes in each molecule
What are the ways myoviridae can be joined
RCR linear phases joined st ends 1-10 (concatamers)
Sticky ends cut precisely
Or
Package more than one genome worth 1-10 and 1-2 of next
What is the Phage P1: lysogenic phage
Pro-phage is plasmid
It’s not integrated into host chromosome (just stays inside cytoplasm as a plasmid)
1 or 2 copies of plasmid exist per cell, which are copied at cell division
Phage encodes special stability functions to ensure (one copy goes to each cell) plasmid not lost from cell so virus persists
Phage P1 - transduction induction to lyric phase
P1 nuclease digests host cell genome (nucleases cuts DNA)
- bacterial DNA is cut at random places
Pieces of bacterial genome about same sizes as P1 can be accidentally packaged into viral particle
What do phage particles act as in transduction
Phage particles now act as a way of transferring bacterial genes between cells
What does phage transfer lead to
New combinations of genes in bacteria
How can a mutation in lysogenic cycle be repaired
Movement to another host cell of same type can repair mutations in genes due to homologous recombination
What is phage P1 variable host range
P1 changes its host range by an invertible DNA region
If fragment switches orientations with promoter at start can express different segments
Switching process can occur randomly in cell
Different cells express different orientation and broadens diversity of where DNA can go
What is the Myoviridae phage like
Temperate lysogenic phage
What is the shape of the myoviridae phage
dsDNA phage with 37 kbp genome
Icosahedral head
Helical tail
6 tail fibres
Phage Mu genome map - C
C gene controls lysis/lysogeny
Phage Mu genome map - A
A gene required for transposition event
Phage Mu genome map - att site
Att site is not a specific sequence, att site defined at end by transposase binding site
Phage Mu genome map - G region
Invertible responsible for host range - can switch host range
What happens to phage Mu after infection
Random insertions of Mu prophage make mutations of host chromosome
What was phage Mu used for
Early tool for insertional mutagenesis E.coli
Why is it called Mu
Phage mutator
How many insertions occur in lysogenic state of phage Mu
One
What controls the phage Mu insertion
C gene
What is the phage Mu life cycle
Linear DNA enters cell via phage particle
Mu DNA inserted into recipient genome via non-replicative ‘cut and paste’ mechanism
- causes duplication of 5 np of host DNA
transposition mediated by A protein
What are he possible effects of Mu lysogeny on host cell
- Deletion by recombination between two Mu genomes or transposons in same orientation
- Inversion by recombination between two Mu genomes or transposons in opposite orientations
How does a deletion by recombination occur
Pairing of Mu genomes or transposons
Crossover
Homologous recombination makes deletion
Deleted segment and chromosome each contain one Mu genome or transposon
How does an inversion recognition occur
Pairing of Mu’s or transposons in opposites orientations
Pairing of Mu’s or transposons
Crossover
Homologous recombination makes inversion
Reversed inverted segment
Wild type Mu in phage Mu life cycle
Wild type Mu lysogeny are stable and not induced by UV or other DNA amazing agents
What happens when C is inactivated in phage Mu life cycle
A and B proteins are expressed
When is Ts mutant inactivated
Ts mutant C inactivated at 42degrees
C falls apart
Why does the cells in Mu life cycle mutate
Cell dies due to number of mutations
What are the late gene products made in Mu life cycle
Includes phage capsids, tails, lysis proteins
