130 
EVENING SESSION 
DR. FREDRICKSON: Good evening. The meeting will please return to order. 
We will commence this evening's proceedings with a presentation on eukaryotic 
host vectors by Dr. Wallace Rowe of the Recombinant Advisory Committee. 
Dr . Rowe . 
DR. ROWE: I will really be speaking on two sections out of the contain- 
ment requirements — that is, on the use of viral inserts in prokaryotic sys- 
tems — that is, pieces of the genomes of animal viruses inserted into E. coli 
— basically, and also the containment levels for animal viruses when used as 
vectors for foreign DNA in cells of eukaryotes in tissue culture. I thought, 
by way of background, since this is a rather highly technical set of guidelines, 
to give a little bit of background on the science of it. I have a few slides 
if we can figure out how to run the machine. 
This is just diagrammatic of the basic structure of viruses — that basi- 
cally all viruses are a protein shell surrounding a nucleic acid genome. 
The nucleic acid is that little wiggly thing in the center, and it generally 
codes for anywhere from 6 to 50 proteins, and although viruses are very 
small, being of the order of 100 millimicrons average in cross-section or 
diameter, they are very complex. They have a number of different proteins 
that are inserted in very orderly array to make up this protective protein 
shell. The nucleic acid is the infectious portion; the protein does not 
contribute to the heredity. In some cases of viruses, the nucleic acid 
alone can infect cells and produce all of the proteins and progeny nucleic 
acid and result in new virus formation. In many other cases the nucleic 
acid is not infectious by itself, but has to have enzymes that are carried 
in the virus particle or other specifications that the virus doesn't carry. 
Now, an important class of viruses are those on the right. Many viruses 
pick up a cellular type membrane, the double-layered membrane that is pinched 
off from some cell membrane. I am talking about eukaryotic viruses now. It 
has glycoproteins on it. The envelope is necessary for the infectivity of 
these viruses, and it is an envelope that is totally dissimilar from the 
bacterial cell wall. It is a safety feature which we have not incorporated 
in the Guidelines, but I think eventually it will be a very significant 
safety feature. There is just no way anyone can imagine that a virus with 
an envelope could be synthesized in toto in a prokaryotic cell. 
The next slide shows just a classification of the types of genomes. 
We can break them down into three types. The genome can be either DNA or 
RNA. In all DNA viruses that I know of, the genome is one chromosome. All 
of the genes are in one linear nucleic acid sequence. In some RNA viruses, 
the genome is one molecule; but there are others, including influenza, and 
in particular reoviruses, where the genome is three to ten chromosomes-- 
essentially, three to ten different segments, all of which are needed for 
infectivity. And we have used, as we will mention in a little bit, this 
difference between a single molecule genome and a segmented genome as a 
safety feature, in that the chance of doing anything with these segemented 
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