MIC 115 Lecture 13: Viral Vectors

Vehicles that deliver DNA or RNA directly into cells, often developed from viruses with all harmful genes removed.

Retroviruses with single-stranded RNA genomes that integrate into the host genome. Lentiviruses can infect non-dividing cells.

Involves converting RNA to DNA, integrating into host DNA, and making new viruses.

Use double-stranded DNA, do not integrate into the host genome. They are large.

Have single-stranded DNA genomes, small size, and do not integrate into the host genome.

The process of introducing genetic material into cells using vectors or carrier molecules.

Using genetic material to treat diseases.

A type of retrovirus that can infect non-dividing cells, known for long incubation periods and potentially chronic diseases.

The process of inserting DNA into a host genome as a provirus, usually by a viral vector.

Modified viruses that use their own integration machinery to stably insert genes into a host chromosome.

They can efficiently and stably integrate genes into cells that are difficult to directly transfect.

LTRs are essential for integration of proviral DNA and initiating viral RNA synthesis.

It ensures proper packaging of the viral genome into new viral particles.

The GAG gene encodes structural proteins that form the nucleocapsid, the core of the virion.

The POL gene encodes reverse transcriptase, an enzyme crucial for converting viral RNA into DNA.

The ENV gene encodes glycoproteins that embed within the viral membrane, allowing attachment to host cells.

The process where double-stranded proviral DNA randomly integrates into the host cell's genome. This integration is essential for the retrovirus to replicate and spread.

Long Terminal Repeats (LTRs) are essential for the integration of retroviral DNA. They act as landing sites for the viral integrase enzyme, which facilitates the insertion of the proviral DNA into the host genome.

Many retroviruses need the host cell to undergo mitosis (cell division) to effectively replicate. This is because the pre-integration complex, which contains the viral DNA, cannot get through the nuclear pore (a gateway to the nucleus) during the cell's resting phase.

Lentiviruses, a specific type of retrovirus, have the ability to infect both dividing and non-dividing cells. They achieve this through viral proteins that actively transport the pre-integration complex into the nucleus.

Viral vectors are tools used to introduce genetic material (DNA or RNA) into cells. They are derived from viruses, but are modified to be replication-incompetent and safe for use.

These vectors are modified versions of viruses where the genes responsible for viral replication have been removed. They can still enter cells and deliver genes, but they cannot make new viruses.

To ensure safety, the essential genes for viral protein production (gag, pol, env, rev) are separated into different plasmids. This prevents the production of new infectious viruses from the viral vectors.

The Ψ sequence is critical for packaging viral DNA into new viral particles. A transfer plasmid containing the gene of interest must have the Ψ sequence to be packaged.

Replacing the Env glycoprotein of a retroviral vector with the Vesicular Stomatitis Virus Glycoprotein (VSV-G) to broaden the range of cell types the vector can infect.

VSV-G interacts with a general phospholipid component of the cell membrane, allowing entry without the need for specific protein receptors.

Retroviral transduction may not be the ideal choice for cells that can be easily transfected or when high transgene expression is needed. They are also limited in the size of DNA they can carry.

Adenoviruses have a double-stranded DNA genome and remain in the nucleus as an episome (not integrated into the host genome).

AAV has a small, single-stranded DNA genome, and does not integrate into the host genome.