Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 160

The translation apparatus is the most highly conserved of all the cellular components. The structures of ribosomes, translation factors, aaRS enzymes, tRNAs, and the genetic code itself have changed remarkably little in billions of years of evolution. This is why these components have been used extensively in molecular phylogeny. By comparing the sequences of the rRNAs and other components of the translation apparatus and determining how much they have diverged, it has been possible to establish phylogenetic trees that include all organisms on Earth. The high level of conservation probably also explains why so many different antibiotics target the translation apparatus compared to other cellular components. An antibiotic designed to inhibit translation in one type of bacteria will probably inhibit translation in many other types of bacteria.

The conservation of components of the translation apparatus is so high that “rooted” evolutionary trees can be made that include eukaryotes and archaea (see the introduction). Such trees are usually not too different from what has been obtained from physiological and other comparisons, but there are sometimes surprises. Also, the sequence of the translation elongation factors led to the suggestion that the archaea are more closely related to eukaryotes than they are to other bacteria, prompting the change of their name to archaea from the original designation “archaebacteria.”

Many of the initiation and elongation factors in bacteria have counterparts in archaea and eukaryotes. Nevertheless, the major differences in the translation apparatus come in the translation initiation factors. While bacteria have only three initiation factors (some of them have more than one form), archaea and eukaryotes have many more. As is the case with other cellular functions, archaea share more of their initiation factors with eukaryotes than they do with bacteria. Also, some of the initiation factors, while conserved, seem to have somewhat different functions in the three kingdoms of life. These differences may reflect differences in the initiation sites for translation.