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17 Cards in this Set

  • Front
  • Back
-small self-replicating RNA pathogen
-autonomous replication
-no capsid
-246-375nt genome, ssRNA
-do not encode proteins
-some possess hammerhead self-cleaving structures
-mostly plant pathogens
-causative agent potato spindle tuber disease (PSTV)
-rely on host enzymes, DNA-dependent RNA polymerase for replication + and - strands, manipulates the RNA polymerase (usually copies dsDNA)
-mechanism pathogenesis unknown
-intramolecular base pairing forms commplex secondary strctures which can be denatured into circular form
-two groups: Class A and B
-genome transfered from cell to see is +
Satellite RNAs
-small self-replicating RNA pathogen
-require helper virus for replication
-200-1700 nt genome
-may encode a protein
Viriod-like plant satellite RNAs
-small self-replicating RNA pathogen
-encapsidated by helper virus proteins
-do not encode proteins
-possess hairpin or hammerhead self-cleaving structure
Hepatitis Delta Virus
-small self-replicating RNA pathogen
-encapsidated by hepatitis B virus protein
-1700 nt, circular, -ssRNA
-encodes delta antigen within virions to form ribonucleoproteins
-possess delta ribozyme activity (delta motif) for self-cleavage
-only knonw self-replicating RNA human pathogen
-"defective virus", relies on HBV for completion life cycle
-only found in patients coinfected by acute or chronic HBV, uses HBV surface antigen, HBsAg, to package its genome
-circular anti-genome encode, not express, delta antigen ORF, poly-adenylation signal and self-cleavage site
-replicates via symmetrical rolling circle using RNA polymerase II in conjunction with delta antigen and cellular factors
Small self-replicating RNA pathogens
-four infectious agents
-differ in replication strategy, structure, coding capacity and self-cleaving catalyitic ability
Potato spindle tuber disease
-caused by class B viriods
Class A Viriods
-self-cleaving RNA due to ribozyme activity
-replicate in chloroplasts via symmetric rolling circle using chloroplast DNA-dependent RNA polymerase
-catalytic ribozyme site possess Group I consensus sequence and 3 important conserved stem loops (similar group I introns in euk.)
-self-clevage carried out by hammerhead strcuture formed by 3 conserved stems
-cleavage site in handel of hammerhead at head attachment
Class B Viriods
-RNA does not self-cleave
-highly conserved central region that is intensively internally base paried giving rod-like secondary structure
-replicate via asymmetric rolling circle using host cell RNA polymerase II
Symmetric Rolling Circle Replication
-class A viriods
-uses chloroplast DNA-dependent RNA polymerase
-+ and - strands replicated same way through circular templates
-HDV uses RNA polymerase II in conjunction with delta antigen and cellular factors
Assymetric Rolling Circle Replication
-class B viriods
-uses host RNA polymerase II
-- strand replicated from circular template
-+strand replicated from linear template
Ribozyme active sites
-conserved sequences and stem loops
Group I introns
-in eukaryotes
-encode nuclear and non-nuclear rRNA, mitochondrial mRNA, chloroplast tRNA
-16 nt consensus sequence, 3 sets complementary sequences
-self-cleave from exons, may subsequently circularise
-parallel evolutio to class A viriods?
Small self-cleaving ribozymes mechanims
-activation 2' hydroxyl adjacent to scissile phosphate by removal of its proton
-attack by 2' oxygen on adjacent phosphate group resulting in separation two sugar moieties and 2',3'-cyclic phosphate on one of sugars
-5' oxygen on other sugar stabilised by incoming proton
-HBV surface antigen used to package HDV genome
-anti-HbsAg antiboties protective against HDV infection b/c it is so dependent on HBsAg
-anti-HDV reactions occur before anti-HBsAg infections
Hepatitis Delta Antigen
-encoded by separate linear mRNA generated by interruption transcription of genomic RNA of HDV; also encodes polyadenylation signal
-post-transcriptional modification of mRNA leads to 2 forms: small (deltaAgS) and large (deltaAgL)
-both contains nuclear localisation signal, RNA-binding regions, dimerisation region
-dimmer required to enable HDV RNA replication and genome packaging
-assocaites with genomic RNA to form ribonucleoproteins that are enveloped by HBsAg to form HDV virions
RNA enzymes
-many enzymatic roles
-self-cleaving ribozyme, RNA ligase, transaminases, tRNA maturation enzymes
-synthetically generted hc ligase can play many roles
-slight modifications secondary strctures can change enzymatic function
-hammerhead ribozyme's ribonuclease can be transformed into an RNA ligase with a disulphide bond
hc ligase
-also has polymerase activity on very small substrates 1-2 nt in size
-RNA enzyme