6 retroviruses Flashcards
(32 cards)
retrovirus viron structure?
is there an envelope?
what is the genomic material like?
it is enveloped
and the matirix is under a lipid bilayer.
there are 2 copies of the + ssRNA
retrovirus
what is differenet about its gemonoic material?
it has 2 copies of + ssRNA
it is the only virus that is diploid.
C) Simple retrovirus genomic organization!
what is R for?
what is the U5 for?
R is for repeat because it is onboth ends.
U5 is for unique to the 5’end.
C) Simple retrovirus genomic organization!
what is the gag gene?
encodes the gag proteins MAtrix, CApsid, NucleoCapsid, and
PRotease. The proteins are made as a polyprotein that then gets clipped (see
below) - NOTE: in some viruses, like HIV, PR is in the pol gene reading frame!
Simple retrovirus genomic organization!
what is the pol gene for?
the polymerase (pol) gene: encodes reverse transcriptase (RT) and integrase
(IN), which are made as an extended polyprotein (see below)!
retorvirus genomic organization
what is the env gene for?
encodes the env protein, which is made as a precursor
and gets cleaved into the surface (SU) and transmembrane (TM) domains (in
HIV, gp160 -> gp120 and gp41, see below)!
retrovirus genomic organization?
what is the U3 for?
it is unique to the 3’ end.
HIV has complex retrovirus organization what does this mean?
Organized similar to simple retroviruses (w/ gag / pol / env), except numerous additional genes / proteins.!
The first phase (steps A-E) precedes integration
what are those steps?
A- Adsorption !!
B- Penetration and uncoating!
C- Reverse Transcription!
D- Transit to the nucleus!
E- Integration into host DNA!
the second phase (F-J) is post- integration.!
F- Viral RNA synthesis, host pol II! G- RNA processing!
H- Virion protein synthesis!
I- Assembly and budding!
J- Capsid maturation (proteolysis)
Adsorption: step?
what happens?
virus binds to cell via the env protein.
hiv uses cd4/CCr5
B. Penetration* and uncoating
what happens?
Viral envelope fuses with cell
membrane either i) at the cell!
surface or ii) in endosomes after endocytosis: *two antivirals to this step*, as will be discussed later!
THE GENOMIC RNA is only partially uncoated.
it remains in a protein particle in the cytoplasm
YOU DONT WANT TRANSLATION AT THIS POINT BECAUSE YOU ARE IN THE CYTOSOL AND YOU HAVE SSRNA
YOU WANT TO MAKE dsDNA and integrate it in to the cells genome.
what converts ssRNA to dsDNA?
reverse transcriptase
what is the integrated DNA called?
what is the long terminal repeats called?
the provirus it is longer than the template RNA b/c it has U3 and U5 repeated at the ends.
LTR are U3 and U5 repeated at the ends.
so it is U3 R U5
where does the reverse transcriptase act?
it does its work in the cytoplasm.
what are the polymerase activites of the reverse trascriptase?
– an RNA-dependent DNA polymerase (copies RNA to DNA)!
– a DNA-dependent DNA polymerase (copies a 2nd strand of DNA from the first strand)!
– is an ‘error prone’ polymerase, ~5 errors per made per genome, which accounts
for rapid evolution and drug resistance!
!
what protein carries out the integration of the cell with the virus?
what sequence does integrace recognize?
can most retroviruses cross the nuclear membrane?
integrase (IN)
it recognizes the end sequences U3 and U5
no most cannot. HIV can though.
what drug atacks Reverse transcriptase?
AZT
what drug attacks integrase?
Raltegravir
integrase is the only protein that causes the virus to get included in the host genome. that is why it is a good target.
what is the major role of the LTR?
where is the binding site?
where does the transcription begin?
to direct synthesis of viral RNA.
the 5’ U3 has the binding sites for the cellular transcription factors.
R is where the transcription begins.
what are the 2 fates of the full length RNA?
what happens to the RNA that is spliced?
they can become genomic RNA
or gag-pol RNA
spliced RNA can go on to make env RNA
how is just gag made?
how is gag-pol made?
what on happens more often?
gag has a AUG start and a stop codon at the end of gag
starts at the gag AUG start and ignores the gag stop.
more often there is a just gag is made and only 5% of the time is gag-pol made.
what breaks up the gag-pol polyprotein?
PR
only outside of the cell once it has budded off.
Both the gag and gag-pol proteins are eventually cleaved by the protease (PR) domain, releasing the individual proteins!
what needs to happen to the env protein?
it is made from spliced mRNA
in ER bound ribosomes
has to go thorugh the ER and golgi to be insereted in to the plasma membrane.
