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According to National Geographic, there are 23 proteins that are common to all life forms:

All species in all three domains share 23 universal proteins, though the proteins' DNA sequences—instructions written in the As, Cs, Gs, and Ts of DNA bases—differ slightly among the three domains

According to NCBI there are 324 proteins common to all life forms.

How many proteins are common to all life forms, and what are their names?

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It must be 23 amino acids. Amino acids are structural units of proteins. Can you cite the material that said 23 proteins are common to all life forms? –  piscean_1993 Jun 26 at 6:13
    
what do you mean by common.. there are homologous proteins.. would you consider them as common? –  WYSIWYG Jun 26 at 6:20
    
There are 324 proteins in M. jannaschii, with at least one homologue present in some species from both the other two domains, Bacteria and Eukarya ..... I don't think the NCBI article you cited is talking about proteins common to all life forms. –  The Last Word Jun 26 at 6:46
    
I am skeptical about 324 as well because an organism named Tremblaya princeps apparently has only 120 protein coding genes. nytimes.com/2013/07/04/science/… –  The Last Word Jun 26 at 7:00
    
I would have thought Ubiquitin would be in the list, considering its derived from the word ubiquitous. –  Venkat Jun 26 at 10:18

1 Answer 1

This question is based upon a wrong inference about the work that forms the basis of the National Geographic article, which includes this statement:

All species in all three domains share 23 universal proteins, though the proteins' DNA sequences—instructions written in the As, Cs, Gs, and Ts of DNA bases—differ slightly among the three domains (quick genetics overview). The 23 universal proteins perform fundamental cellular activities, such as DNA replication and the translation of DNA into proteins, and are crucial to the survival of all known life-forms—from the smallest microbes to blue whales.

The article is referring to a paper published in Nature in 2010.

http://www.ncbi.nlm.nih.gov/pubmed/20463738

This paper uses a set of 23 proteins to test the idea that certain genes arose only once.

The data set consists of a subset of the protein alignment data from ref. 27, containing 23 universally conserved proteins for 12 taxa from all three domains of life, including nine proteins thought to have been horizontally transferred early in evolution27. The conserved proteins in this data set were identified based on significant sequence similarity using BLAST searches, and they have consequently been postulated to be orthologues.

There is no suggestion that there are only 23 such proteins, it's just that the author chose this subset to test his ideas.

And here they are:

alanyl-tRNA synthetase, aspartyl-tRNA synthetase, glutamyl-tRNA synthetase, histidyl-tRNA synthetase, isoleucyl-tRNA synthetase, leucyl-tRNA synthetase, methionyl-tRNA synthetase, phenylalanyl-tRNA synthetase β subunit, threonyl-tRNA synthetase, valyl-tRNA synthetase, initiation factor 2, elongation factor G, elongation factor Tu, ribosomal protein L2, ribosomal protein S5, ribosomal protein S8, ribosomal protein S11, aminopeptidase P, DNA-directed RNA polymerase β chain, DNA topoisomerase I, DNA polymerase III γ subunit, signal recognition particle protein and rRNA dimethylase

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This answer was downvoted - I'd be really interested to hear why. –  Alan Boyd Jul 2 at 21:15

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