Journal Watch: MHC and intracellular self

Shiv Prasad shiv at htlv.med.umn.edu
Mon Aug 24 13:14:31 EST 1992


In article <92237.091833FORSDYKE at QUCDN.QueensU.CA> <FORSDYKE at QUCDN.QueensU.CA> writes:
>>
>   Forsdyke: So, we agree that parts of the gene, both the protein-
>             encoding part and other parts, can be acted upon by
>             evolutionary forces to affect (i) specific function, (ii) quant-
>             ity, and (iii) distribution (compartments or complexes) of the
>             gene product (protein). [The ability to be modified is also a
>             function of the protein sequence and this may affect (i) to (iii)]
>                For simplicity, as in our initial test-tube model, we can
>             consider (i) and (ii) in relationship to the cytosolic compartment
>             The evolution of specific function and protein concentration can
>             be considered independently. The protein has a theoretically
>             possible maximum specific activity (activity/unit protein). There
>             is a minimal level of activity needed by the cell. So this sets
>             the lower limit on protein quantity. As this quantity rises above
>             this lower limit the specific activity can decrease and still
>             maintain the same level of function. So gene is free to respond to
>             evolutionary forces affecting protein quantity, without compromis-
>             ing function. Do you accept all this? If so, would you care to
>             speculate what evolutionary forces would determine that a
>             particular gene evolve to set a particular protein concentration
>             within a particular cytosol?
>                   Sincerely, Don Forsdyke
>

I just bought a copy of "The Selfish Gene" this weekend, and haven't had the 
time to read it yet (yes, I know I should have read it years ago).  Maybe the
answers to everything are written within.

The cytosolic concentration of a protein would be determined (teleologically
speaking) by necessity.  For example, organisms in a certain environment would
need certain proteins more that organisms in other environments, e.g. DNA-
repair proteins may be in higher concentration in bacteria exposed to high
UV rays, or other radiation than in the average lab strain of E. coli.  It
could be as simple as selection for those that express the appropriate level
of that protein to survive.  Let's take UV rays as a speculative example.
Normally they would damage DNA, but the one-cell-in-a-billion whose
exposure to UV leads to an up-promoter mutation in the DNA repair operon
would have a selective advantage over the others, and may eventually survive,
thereby creating a radiation-resistant organism.

Perhaps an extreme sink-or-swim example, but the bottom line is if mutation
fulfills a need and leads to a competitive advantage, that is the 
evolutionary force that would control cytosolic concentrations of various
proteins.

Shiv
>>>>>>>>>References:   Forsdyke, D. (1992) Bionet.immunology 812 947edt
>>>>>>>>>              Prasad, S. (1992) Bionet.immunology 814 1516gmt
>>>>>>>>>              Forsdyke, D. (1992) Bionet.immunology 817 1757edt
>>>>>>>>>              Prasad, S. (1992) Bionet.immunology 818 133gmt
>>>>>>>>               Forsdyke, D. (1992) Bionet.immunology 818, 1616edt
>>>>>>>                Prasad, S. (1992) Bionet.immunology 819, 405gmt
>>>>>>                 Forsdyke, D. (1992) Bionet.immunology 819 1019edt
>>>>>>                 Prasad, S. (1992) Bionet.immunology 819, 2019gmt
>>>>                   Forsdyke, D. (1992) Bionet.immunology 820, 858edt
>>>>>                  Prasad, S. (1992) Bionet.immunology 821, 56gmt
>>                     Forsdyke, D. (1992) Bionet.immunology, 858 edt
>>                     Prasad, S. (1992) Bionet.immunology 821, 1544gmt



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