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List the following proteins in the order of decreasing evolutionary conservativeness of their primary structure:

  1. Somatotropin.
  2. Catalytic subunit of a DNA – polymerase.
  3. Histone H1.
  4. Prolamines (storage proteins of cereals).

What I think : I am sure that 4th one should be last. I believe that H1 sequence is not that important as I had read somewhere that a cell can survive even without H1 histone. I also think that catalytic subunit is most important. So, according to me the order should be : 2,1,3,4.

Am I right ?

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I believe it should be 2,3,1,4, since the histones are involved in several epigenetic regulations, lyonisation and transcriptional regulations, and since these regulations greatly change the phenotype under consideration, I think conserving the histones' primary structure should be more favourable as compared to Somatotropin, since slight modifications in hormones might not affect much due to absence of perfect specificity, presence of hormones with supplementary action, and so on. –  Satwik Pasani Jan 27 at 14:51
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Do you think so? It would still be something like a comment. –  Chris Jan 27 at 16:34
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@Chris I guess Unless there are any publications to provide data on the conservativeness of these proteins' primary structure, your comment is the best answer that can be given, as far as logical reasoning is considered. –  Satwik Pasani Jan 27 at 17:51
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Ok, if you say so...I can have a look if there is some data available later. –  Chris Jan 27 at 18:37
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This is such a crappy question (not yours @biogirl, your teacher's). You cannot answer this question without actually checking the sequences. For example, the cell can survive without H1, OK, but H1 cannot function without it's structure since it's function is very dependent upon the structure. Therefore, it would not surprise me if it were exceedingly conserved. The question is an example of a lazy teacher, all you can offer is conjecture. –  terdon Jan 29 at 16:33
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up vote 3 down vote accepted

Even when you can live without Histone H1, its a widely distributed protein which you find in basically all living cells (except for some yeasts if I remember correct). This points to the fact that it must be available for quite a while. The same is true for the catalytic subunit of the DNA polymerase. Somatropin is still pretty important (and can be found in a lot of organisms), prolamines are quite specific to certain cereals. I would group it 2-3-1-4.

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bacterial requirements for histones is not as great as euks I would say - what cell can reproduce without DNA polymerase? –  shigeta Jan 28 at 5:45
    
@chris Does conservnativeness mean that it is present in most organisms or does it mean that the sequence/structure is not changed? –  biogirl Jan 28 at 7:44
    
@shigeta hats why I think that the DNA polymerase is higher conserved. But the histone comes next. –  Chris Jan 28 at 7:51
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@biogirllajja It can mean both :-) And its connected - proteins which are old in an evolutionary sense (like a DNA polymerase or something like cytochrome P450) are also highly conserved (for structural and functional motifs) on the sequence level. –  Chris Jan 28 at 7:57
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