DNA Virus Replication

Question 1

General Comments

Answer 1

*Replication of viral DNA occurs in the nucleus (b/c thats where enzymes req’d for replication) except for poxviruses which replicate entirely in the cytoplasm (b/c they have necessary enzymes w/ them)
*Host functions expressed during S phase needed for viral DNA replication
*Availability of host cell DNA binding proteins for transcription help determine tissue trophism and host range of virus
*Some DNA viruses cause non-productive (latent) infections
*All DNA viruses except parvoviruses can transform cells

No antivirals used for herpes cure latent infections…

Question 2

Nuclear DNA Viruses

Answer 2

*Adenoviruses, herpesviruses, and papovaviruses have a double-stranded DNA genome
*Some strains of all three types can transform cells
*Hepadnaviruses have a partially double-stranded DNA genome (Hep B)
*replicate their DNA in the nucleus via a RNA intermediate
*involve a RNA-dependent DNA polymerase (reverse transcriptase) in their replication
*Can transform cells

Should not be surprising that Heb B can be tx w/ drugs developed for HIV

Question 3

Hepatitus B:

DNA enters cell; uncoats, enters nucleus.

RNA copy then goes to cytoplasm of cell

Reverse DNA transcriptase then makes partially double-stranded DNA in cytoplasm from RNA.

Evidence suggests, that if RNA doesn’t leave nucleus, hepatocyte can be transformed into cancer cell; replicate

Answer 3

Question 4

Nuclear DNA Viruses, ctd.

Answer 4

Parvoviruses have a single strand DNA genome
enters nucleus through nuclear pores
single-stranded DNA forms hairpin structure which self primes cellular DNA polymerase to synthesize complimentary strand
double-strand DNA uses cellular DNA polymerase and viral specific endonucleases to form genome DNA
some strains need a helper virus to replicate (e.g., adeno-associated virus)

..Some viruses need helper viruses

Question 5

Cytoplasmic DNA Viruses

Answer 5

Poxviruses have a double-stranded DNA genome
Provide their own mRNA and DNA synthetic machinery
Code for viral DNA dependent RNA polymerase and mRNA modifying enzymes for processes like capping and methylation
Poxviruses synthesize their own envelope

Most DNA viruses are icosahedral and replicate in nucleus. Pox is excetption b/c it has DNA
dependent
RNA
polymerase