Precise Similarity of Many Human Proteins to Proteins of Prokarya

Abstract

Proteins originated in early forms of life and have long survived, because they have always been required. Some recognizably similar proteins are found in all sequence comparisons between species, no matter how distant, including prokaryotes and eukaryotes. Reported here are observations on the relationships of human proteins to the proteins of 458 prokaryotes for which protein libraries are available. Each of these libraries includes a protein that matches a human protein with a BLAST score of 573 or more, indicating excellent conservation of certain amino acid sequences. A majority of these proteins also match a yeast protein and other eukaryote proteins with comparable accuracy, indicating that protein conservation is responsible in most cases rather than the horizontal transfer (HGT) between eukaryotes and prokaryotes. Rare examples of HGT are apparently also seen. Very many significant matches are seen as the criterion is opened, including 20,596 human proteins that match at least one prokaryote protein with expectation of 10-3 or less. Individual prokaryote proteins accurately match parts of many modern human proteins that have a wide range of functions showing directly that many proteins of different functions have evolved from an ancestral protein by duplication, rearrangement and divergence of function. The implication is that most or all modern proteins derive from the proteins of the last common ancestor with prokaryotes through many such events.