Saguaro Measles Virus

The Saguaro Measles Virus

Your departmental writing requirement is to write two papers on assigned themes. The first of your assignments will be to write a paper in the style of a journal article. It should have all of the sections required of such articles. However, in this first one, references will not be emphasized because the theme is purely fictional as it encompasses Mary Lou's saga of the saguaro measles virus. The difference is that you are to pretend that you are working with her group and together you have done the research and are now writing this paper. You may consult with the other members of your group about the "meat" in this paper - what should be included and what excluded, what conclusions to make and what discussion topics you want to include. All their names (and not those of Mary Lou and friends) are to be given in the author list. Only one point: YOU must write the paper, and place an astericks ("*") after your name. After the instructor has reviewed, annotated and returned your paper, you are to revise it and hand it in again. The revisions will continue until your "editor", the instructor accepts it as final draft. At that time you will submit two copies of the paper - one with only your name on the author line, and the other with all your group members' names.

In order to have some sort of uniformity within this hypothetical virus's realm, here are a few factlets about "SMV".

The mythical saguaro measles virus (SMV) is an RNA virus with a genome that has one of these overall structures:

Each of these has about 1/3 of itself in the form of a double helix. These semi-dsRNA genomes were found to be so by combining several techniques: hyperchromic studies, and use of RNase1 and RNase2 and showing that neither could destroy the whole genome. These may be divided into two groups:

  1. Those consisting of only one strand of RNA that fold back upon itself in places (a, b and c) due to palindromes, and
  2. Those consisting of more than one strand of RNA (d and e).
What evidence do we have that would support or deny any of these alternative structures?

The next thing to be considered is that the palindromic part is complementary to a portion of the host's DNA - an allele, as it were. So suppose that you straighten out the palindromic portion of the RNA genome, reverse-transcribe it to DNA and then match up the allelic portions of the viral and host DNA's. Here is one example where this has been done with alternative "c":

You see that this cannot work because you have two unattached "ears". Nature insists that the integrated structure be LINEAR. So try integrating the other alternative structures of the viral genome.

The interesting thing about this virus is that it has two pathways it can take depending on the environmental conditions. If the temperature is high, the virus remains active and replicates in the cells and kills the cells. However, at cooler temperatures, the virus reverse-transcribes and integrates into the host's DNA and remains there domant until such a time that the temperature rises above some degree that causes the repressor to inactivate. In the following diagram, the left side shows the viral genome (middle) undergoing integration and dormancy (what bacterial virologists call "lysogenic"). The right-hand side shows what bacterial virologists would call "lytic phase".

There are many open questions remaining. This is "good" because a virologist without any more questions to answer would become a hungry virologist! Also it is good for you as the author of a paper for the departmental writing requirement because it gives you things to write about in your "discussion" section. Let's touch upon two of these open questions:

I want to go to the TOP OF PAGE or ESCAPE! or go back to the Virology Home Page!