Adenoviruses

Question 1

Adenoviridae

Answer 1

non enveloped, 12 projecting spikes which bind to cell surface receptors; terminal protein on 5’ end

Question 2

Genome

Answer 2

linear double stranded DNA; unusual feature is the presence of a virus encoded 55kDA terminal polypeptide (TP) to dCMP at each 5’ end of the genome along with an origin of replication; 8 RNA pol II and 3 RNA pol II transcriptional units; translation involves immediate early, early, and late genes; lots of splicing; NOT oncogenic in humans but is in rodents; E1B and E1A re oncogenic; E1 binds to p53 and E2B is the DDDP

Question 3

Attachment

Answer 3

Cell receptor is 46 kDA immunoglobulin called CAR; alternative receptors have been identified such as Aden type 2 binds to MHC I on epithelial and B cells and Aden Type 5 binds to integrin alpha m Beta ; primary infection between fiber knob and primary receptor followed by a second interaction of penton base RGD and cell interns which trigger receptor mediated endocytosis

Question 4

Uncoatin

Answer 4

multiple steps in which viral capsid proteins removed in endosome where the fiber protein IIIa and VIII dissociate from capsid; endosome is acidified which causes the release of the pentane base and protein IX and protein VI is degraded in endosome by viral protease L3/p23 which is in core of virion; L3/p23 is inactive in virion; conformational change occurs in protein VI following interaction of pentane base to intern receptor which exposes L3/p23 cleavage sites; the pentane base is thought to mediate lysis of endosome; the capsid which is now devoid of all components except the core proteins, DNA and small amounts of heron protein docks to nuclear pore and is released in nucleus

Question 5

Replication

Answer 5

Assembly of viral pre terminal protein (pTP) and DNA pol complex (E2) into pre initiation complex at each terminal origin of replication results in covalent link of dCMP to serine residue in pTP; cell transcriptional cofactors Nf1 and Oct 1 facilitate assembly by binding to viral replication proteins; free 3’ -OH group of pTP-dCMP complex primes continuous synthesis in 5 - 3 direction; reaction also requires E2 product and cell topoisomerase; since terminal segments of the viral genome comprise an inverted repeat sequence there is an origin at each end and both parental strands can be replicated by this displacement mechanism; reannealing of complementary terminal sequences of the parental strand displace in single stranded form during the initial step forms a short duplex stem identical to the terminus of the ds genome the reformed origin directs a new cycle of protein priming and continuous DNA synth

Question 6

Replication

Answer 6

DSDNA with an origin of rep on each end
System is primed for replication via TP-dCMP
Strand displacement replication: 5 tp 3’ and semi circularizes due to inverted repeats and now we replicate the other molecule
Unique features: splicing, fibers, replication

Question 7

Inhibition of Host Functions

Answer 7

Va-RNA 1: inhibits Pkr and INF a/B production
E3 proteins (4): block apoptosis by tumor necrosis factor and Fas, binds to MHC class I antigens and prevents transport to cell surface (inhibits CTL recognition), promotes relate of virus from lysed cells

Question 8

Replication Overview

Answer 8

Transcription and translation of E1A; Following splicing and export to cytoplasm where translated and post translationally modified; imported into nucleus were the large E1A regulates transcription of viral early genes (RNA pol II)
Transcription of VA genes by RNA pol III begins in early phase of infection; VA RNA 1 inhibits per and inf a/b production but fiction of VA RNA II unknown
Early protein include DNA replication proteins which are translated in cytoplasm and imported into nucleus and cooperate with cellular proteins to perform viral DNA synthesis
Late promoters are activated by viral DNA replication but maximal transcription of late genes requires IValpha 2 proteins
Late mRNA selectively exported from nucleus by E1B-55kDa and E4-34 kDa proteins. Their efficient translation requires VA-RNA I (inhibits Pkr as well as INF / production and the late L4 protein. L4 protein also acts as chaperone for assembly of hexons and other structural proteins as they enter nucleus.

Immature noninfectious virions are formed. Mature infectious virions are formed when viral protease (L3) cleaves these precursor proteins.