Background

    The ribosome is, in essence, a molecular factory designed to make proteins according to the genetic message contained in deoxyribonucleic acid (DNA). Before a protein can be made, the necessary information is first copied from DNA into a form which can be read by the ribosomes. This intermediate form is known as messenger ribonucleic acid, or mRNA. Messenger RNA is a molecule in which the linear order of nucleotides (U, C, A, and G) act like code that specify the order of amino acids that are to be incorporated into a protein. The ribosome is the machinery that reads this mRNA code and manufactures the corresponding protein.

Historical Perspective

    Because the translation of information into protein is common to all life, changes in the translational mechanism can reveal much about the evolution of life. Indeed, early studies on the components of the protein synthesis apparatus, ribosomal RNAs, ribosomal proteins, and protein synthesis factors (also proteins), led to attempts to understand the tree relating all organisms, the universal tree of life. In our lab, we were working on the three dimensional structures of eukaryotic ribosomes (Lake & Slayter, 1970) using three dimensional reconstructions from electron micrographs (Lake & Slayter) and through antibody labelling experiments (Lake, 1976). Looking at the resulting micrographs, we noticed the considerable differences in size and structure of ribosomes between yeast, a unicellular eukaryote (Lake, 1970) and E. coli , a prokaryote (Lake, 1976). This observation prompted us to wonder if there was a prokaryote whose ribosomes exhibited a structure that was intermediate to those of yeast and E. coli . We reasoned that an organism with ribosomes that exhibited some features of a prokaryote and some of a eukaryote would constitue some evidence that prokaryotes were the forerunners of eukaryotes. And so we began to search for such an organism -- a search which was meant to gain greater understanding of the origins of the eukaryotic nucleus.