Biomedical Engineering Reference
In-Depth Information
Nucleoprotein
Envelope
Caspid
RNA
Cell membrane
DNA
RT
gpe
RNA
Proviral DNA
gpe
Nucleus
RNA
Figure 14.B1
The retroviral life cycle
gag
(codes for core viral protein),
pol
(codes for reverse transcriptase) and
env
(codes for the viral
envelope proteins). At either end of the viral genome are the long terminal repeats (LTRs), which
harbour powerful promoter and enhancer regions and sequences required to promote integration
into the host DNA. Also present, immediately adjacent to the 5´ LTR, is the packing sequence (ψ).
This is required to promote viral RNA packaging.
The ability of such retroviruses to (a) effectively enter various cell types and (b) integrate their
genome into the host cell genome in a stable, long-term fashion, made them obvious potential
vectors for gene therapy.
The construction of retroviruses to function as gene vectors entails replacing the endogenous
viral genes, required for normal viral replication, with the exogenous gene of interest (Figure 14.4a).
Removal of the viral structural genes means that the resulting vector cannot itself replicate. In
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