Question 1
In contrast to most dsDNA animal viruses, the poxviruses replicate solely in the cytoplasm of the host cell. What does this suggest about the virus?Question 2
A scientist discovers a new virus associated with a cancer. She is able to culture it in the laboratory and begins to analyze it. What features will help her determine the virus' classification? How does this help her understand the virus' mechanism for causing cancer?Answer 1
All cellular DNA replication occurs in the nucleus. DNA polymerases are synthesized in the cytoplasm and are transported into the nucleus where they are active. Replication of viral DNA in the cytoplasm would require DNA polymerase activity take place in the cytoplasm. One possibility is that the viral genome includes a gene for a DNA polymerase and that a DNA polymerase enzyme is packaged in the virion. Otherwise, the virus has some mechanism for diverting cellular DNA polymerase to the cytoplasm. The first possibility is the simpler explanation.Answer 2
Characterization of the nucleic acid present in the virion is a first step in determining the classification of the virus. If it is a large DNA virus with envelope, it may be one of the Herpesviridae. DNA viruses with smaller genome sizes known to cause cancer are the Papillomaviruses and Polyomaviruses. The Hepadnavirdae have a circular DNA molecule which is partially double strand and partially single strand. Very small DNA viruses which occasionally cause cancer are the Adenoviridae. The presence or absence of an envelope is also useful in eliminating possibilities. The presence of a segmented genome comprised of + single-strand RNA and the enzyme reverse transcriptase is consistent with the virus being a member of the Retroviridae.