Re: Re: Re: Eight simple questions and a repeated request to Brian Foley 26 May 2004
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Brian T Foley,
HIV Researcher
Los Alamos National Lab, Los Alamos, NM 87545

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Re: Re: Re: Re: Eight simple questions and a repeated request to Brian Foley

Chris Tyler wrote:
“…In double banding sucrose density gradients they obtained particles "banding in the region of the gradient corresponding to a density of 1.14-1.15 gm/ml". "No apparent differences in physical appearances could be discovered among the viral particles in these regions.”

Yes. We went over those papers in June 2003 (see above in this very same discussion), where I pointed out that although the virus particles did not appear to be different, they were in fact composed of 3 different types. This is because the Moloney murine sarcoma virus does not replicate on its own, it requires a helper virus such as the Moloney murine leukemia virus to produce infectious virions, although non-infectious particles which look identical to infectious particles, can be produced in the absence of helper virus [1]. This paper is a good example of why molecular methods are a very good addition to density gradients and EM.

Retroviruses package 2 copies of the viral genome. Thus a mixture of Mo-MSV and Mo-MuLV produces three different types of viral particles, some with two copies of the Mo-MSV genome, some with two copies of the Mo-MuLV genome, and some with one copy of each genome packaged. In the early 1970s, the exact nature of these processes had not yet been fully characterized (see [1] for example), but after molecular cloning, monoclonal antibodies and other techniques and reagents became available in the late 1970s and early 1980s, much more was learned about retroviruses.


1: Bassin RH, Phillips LA, Kramer MJ, Haapala DK, Peebles PT,
Nomura S, Fischinger PJ.
Transformation of mouse 3T3 cells by murine sarcoma virus: release
of virus-like particles in the absence of replicating murine leukemia
helper virus.
Proc Natl Acad Sci U S A. 1971 Jul;68(7):1520-4.
PMID: 4327005

Competing interests: None declared