Retroviruses Flashcards
RNA viruses that replicate through a DNA intermediate, which efficiently integrates into the genome of permissive cells forming a provirus
Retroviruses
A hallmark of the retrovirus life cycle is the process of
Reverse transcription
The viral RNA genome acts as template for the synthesis of viral DNA by the virus encoded polymerase during
Reverse transcription
Other viruses such as Hepatitis B virus and Cauliflower Mosaic virus utilize
Reverse transcription
The study of Retroviruses has taken on added intensity since the discovery of pathogenic human retroviruses such as
HIV-1 and 2 and Human T-lymphotrophic virus (HTLV-1)
Cause tumors in animals
Oncoretroviruses
Cause a variety of immunological and neurological diseases with a long latency
Lentiviruses
Cause vacuolation of some mammalian cells in culture
Spumaviruses
Surrounded by a lipid envelope derived from the infected cell upon budding of the virus
-Measure approximately 100 nm in diameter
Mature HIV-1 Virion
The virions have spikes emanating from the
Envelope
The spikes are composed of virus envelope proteins, which bind to receptors on permissive cells to initiate
Infection
The core of mature virions is conical in structure in the case of
HIV-1
The core of mature virions contains a round core in the center of the particle in the case of the
Murine leukemia virus
There are additional structures that have been observed for other types of retroviruses. But what is common to them all is that the infectious mature virions contain a condensed core of
Electron dense material
The genome within the core consists of two usually identical single-stranded, positive strand
RNA molecules
The RNA is capped and polyadenylated indicating that it is transcribed by cellular
RNA polymerase II
Most of the cis-acting elements that must be covalently linked to the genome for efficient replication to occur are located at the ends of the
Genome
The trans-acting sequences encoding the viral proteins are located between the
cis-acting elements
The retroviral genome is always organized in the same way as
5’ gag pol env 3”
At each end of the proviral genome (integrated double-stranded DNA) are
Long Terminal Repeats (LTRs)
The long terminal repeats can be funcitonally divided into which 3 parts?
U3, R, and U5
Begins in the 5’ LTR of the provirus at the U3-R border
Transcription initiation
It should be noted that the viral promoter is harbored in
U3
Occurs in the 3’ LTR at the R-U5 border
Polyadenylation
Thus, the single-stranded RNA genome found in virions is shorter than the viral doublestranded
DNA genome
The sequence that is lost during RNA transcription is replaced during
Reverse transcription
They are typically cell surface proteins with the different groups employing different proteins, as such they are important determinants of host range
Retrovirus receptors
A notable retrovirus receptor
-The receptor for HIV
CD4
Found on helper T cells and macrophages helping to account for the HIV host range
CD4 receptor
In contrast to other retrovirus receptors isolated to date, requires a co-receptor
HIV infection
The co-receptors are members of the chemokine receptor family with the most prominent being
CXCR4 and CCR5
Infection is initiated when the envelope glycoprotein SU (surface envelope protein) binds to the corresponding receptor(s) on the permissive
Target Cell