Molecular sleuths track evolution through th...( A new study of the ribosome the cell...)

A new study of the ribosome, the cell's protein-building machinery, sheds light on the oldest branches of the evolutionary tree of life and suggests that differences in ribosomal structure between the three main branches of that tree are "molecular fossils" of the early evolution of protein synthesis.

The new analysis, from researchers at the University of Illinois, reveals that key regions of the ribosome differ between bacteria and archaea, microbes that the researchers say are genetically closer to eukarya, the domain of life that includes humans. The study appears this week in the Proceedings of the National Academy of Sciences.

The findings confirm and extend the early work of Illinois microbiology professor Carl Woese, an author on the study. Woese was the first to look for signs of evolution in the ribosome, where genetic information is translated into proteins. In the mid-1970s, he and his colleagues found consistent differences in the sequence of nucleotides that spell out the RNA of the ribosome in bacteria and archaea. These "molecular signatures" were so pronounced that Woese concluded that the archaea comprised a separate domain of life, distinct from bacteria and eukarya (animals, plants, fungi and protists). His classification system is now widely accepted.

"Carl Woese and his colleagues years ago established that protein translation had to be well developed when the evolution of modern cells started," said Illinois chemistry professor Zaida Luthey-Schulten, an author on the new study. "So the evolution of cells and the evolution of translation are really linked to one another."

The ribosome has two subunits, each made up of RNA and proteins. It interacts with a host of other molecules to guide the assembly of new proteins.

The researchers analyzed the sequence of nucleotides (the building blocks of RNA) and amino acids (the building blocks of proteins) that make up the ribosome.