Questions For Chapter

(b) Adenovirus DNA replication proceeds in two stages. Suppose that you have an in vitro system that allows you to examine features of this synthesis. The reaction mixture has all the required viral and host proteins. Predict the effect of the following modifications on the process of the two stages. Use a "+" sign if the stage will occur normally and a "—" sign if the stage will be blocked by the treatment.

Structure

Possible for adenovirus?

O

„V

-•

o\

—^

Ô

(a) The drawings in the following table represent possible structures for replicating DNA molecules. Indicate which ones might be found if you examined replicating adenovirus DNA isolated from an infected host cell.

Modification

First stage

Second stage

Control (no treatment)

+

+

Removal of the terminal protein from both 5' ends of DNA genome

Removal of the terminal complementary sequences from one end of the DNA genome

Prevention of maturation of terminal protein from 80-kd to 55-kd form

2 Cells that have been infected with adenovirus 2 (Ad2) are treated with the chemicals shown in the accompanying table. In each case, treatment inhibits the

3 A papilloma (wart) virus enters a cell and does not produce progeny virus; however, episomal DNA is maintained within the cell, and some gene expression occurs. Of which kind of infection is this an example?

4 What are the functions of T antigen during the SV40 infectious cycle?

5 Which of the following statements about the life cycle of SV40 is false?

production of progeny Ad2 virus in the cell. Briefly give a reason why the Ad2 life cycle is blocked in each case.

  • a) It expresses three transcripts encoding three capsid proteins late.
  • b) The genome contains a specific sequence of nucleotides that acts as a polyadenylation signal for transcripts using either strand of DNA as templates.
  • c) It has specific promoters controlling expression of early and late transcripts.
  • d) It replicates in the nucleus.
  • e) It replicates using mostly cellular enzymes.

Chemical

Effect on cell

Reason for Ad2 inhibition

NH4Cl

Blocks acidification of secondary lysosomes and endosomes

Vinblastine

Disrupts the microtubular cell

cytoskeleton

Emetine

Inhibits protein synthesis

Replication of Some Nuclear-replicating Eukaryotic DNA Viruses with Large Genomes

  • HERPESVIRUS REPLICATION AND LATENCY
  • The herpesviruses as a group Genetic complexity of herpesviruses

Common features of herpesvirus replication in the host

# The replication of the prototypical alpha-herpesvirus - HSV The HSV virion

The viral genome HSV productive infection

# HSV latency and LAT

HSV transcription during latency and reactivation

How do LAT and other specific HSV genes function - may be to accommodate reactivation?

  • EBV latent infection of lymphocytes, a different set of problems and answers
  • Pathology of herpesvirus infections Herpesviruses as infections co-carcinogens
  • BACULOVIRUS, AN INSECT VIRUS WITH IMPORTANT PRACTICAL USES IN MOLECULAR BIOLOGY
  • Virion structure
  • Viral gene expression and genome replication
  • Pathogenesis
  • Importance of baculoviruses in biotechnology
  • QUESTIONS FOR CHAPTER 17

The term large, when applied to DNA virus genomes, must be relative. The genomes of large DNA viruses encode anywhere from 50 to more than 1000 distinct genes, and on the upper end of size, the viral genomes can contain more genes than the simplest "free-living" organisms: the mycoplasmas.

Much of the genetic complexity of large, nuclear-replicating DNA viruses is due to viral genes devoted to providing the virus with the ability to replicate and to mature in differentiated

CHAPTER

cells, as well as viral defenses against or accommodations to host defense mechanisms. These genes are often not required for virus replication in one or another type of cultured cells, at least under certain conditions, and can be termed "dispensable for virus replication." While this designation is in relatively common use, it is misleading, because no virus gene maintained in a wild strain that replicates efficiently in the population at large is dispensable.

Stripped of "dispensable" genetic functions, a large-genome DNA virus must contain the same essential components as one with a small genome: genes devoted to subverting the cell into a virus-specific transcription factory, enzymes for viral genome replication, and the proteins and enzymes required to form the capsid and to assemble and release new infectious virions. Given these requirements, it is not too surprising that the replication basics of these large-genome, nuclear-replicating DNA viruses follow the same basic strategies as seen with smaller DNA viruses.

It is important to keep in mind, however, that there are many different ways a virus can modify a cell to result in a site favorable for its replication — "the devil is in the details"!

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