Lecture 13 Flashcards
virions (what one) can also acquire envelopes from
anywhere in the secretory system
herpesvirus
virions must get past the
plasma membrane
new virions are created by
assembly of genomes and structural units
enveloped viruses must acquire
an envelope from a cellular membrane (budding)
non-enveloped viruses usually exit through
cellular lysis
early phase DNA virus macromolecular synthesis two types of gene expression
early and immediate early
immediate early genes
expressed without any viral gene expression
early genes
expressed early in infection before the genome replicates
often requires viral gene expression
DNA virus macromolecular synthesis
dsDNA
immediate early - Tc factors
early - TL
DNA replication (genome replication)
late proteins - Tc and TL
viruses have different strategies to
time late replication
early and late DNA virus macromolecular synthesis
early: subvert/take over the host cell, stimulate genome synthesis
late: assembly progeny virions, egress from the cells
early and late replication must avoid
the innate and adaptive immune responses
stimulation of the cell cycle
DNA synthesis occurs during S-phase
a DNA virus can stimulate S-phase or some DNA viruses encode their own DNA synthesis proteins
which viruses can stimulate S-phase
polyomavirus
adenovirus
papillomavirus
what virus encodes its own DNA synthesis proteins
herpesviridae
herpesviruses
large dsDNA (130-220 kb)
enveloped
virions have tegument
replicate in the nucleus
tegument
in herpesvirus virions
loosely associated virion proteins that enter cells during infection
8 human herpesviruses (HHV)
alpha - herpes simplex virus 1/2, varicella zoster virus
beta - cytomegalovirus, HHV-6A/B, HHV-7
gamma - Epstein-Barr Virus (EBV), Kaposi Sarcome-associated Herpesvirus (KSHV)
EBV - mononucleosis, Burkett’s lymphoma
VZV - chicken pox and Shingles
HSV1/2 - cold sores and genital herpes
herpesviruses replication
virions fuse at plasma membrane
capsid travels by microtubule to nucleus
viral mRNA transcribed by Pol II
Immediate early gene Tc/TL: degrades host mRNA, expression of viral Tc factors
Early gene Tc/TL: evasion of host immune response, express viral polymerases to replicate genome
Genome replicates: as a long concatemer by rolling circle replicated
Late gene Tc/TL: capsid proteins to package genome, glycoproteins for envelope
Egress by secretory pathway
why is herpes forever
because it can establish latent infections
how does herpesviruses establish latent infections
alpha herpesviruses infect sensory neurons after lytic replication in epithelial cells
virions travel up axon to soma
viral genome circularizes and is condensed with histones
minimal viral gene expression
stress can stimulate spontaneous expression of IE genes
lytic replication proceeds with virions budding from the axon
virion production is amplified in epithelial cells
papilloma viruses
small dsDNA, non-enveloped
~150 human strains, most low risk
cause genital warts
cause cancer
infection is stealthy
can establish a persistent infection
nine strains of HPV
papillomavirus replication
must infect basal cells near the basement membrane (actively replicating)
replication cycles mirrors stratifying and differentiating epithelium
what can lead to tumourigenesis
persistent E6 and E7 expression due to genomic integration
early proteins E6 and E7 are essential to drive _______, also are _______
S-phase
oncogenes
HIV
Human Immunodeficiency virus
retrovirus… transcribes DNA from an RNA template
how do retroviruses work
each virion has two genome copies
reverse transcriptase is an RNA-dependent DNA polymerase and is packaged in the virion
infects CD4+ cells (T cells and monocytes)
