The Classification of Prokaryotes

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Dr. Carl Woese of the University of Illinois will continue his work toward understanding the natural (phylogenetic) relationships among the myriad species of eubacteria. The evolutionary relationships among species are assessed by determining the degree of similarity (or difference) between ribosomal RNA sequences from one species to another. From a set of (binary) sequence differences - expressed either as percent sequence difference, or in terms of the actual nucleotide positions in the sequence that show differences - evolutionary trees can be constructed by standard statistical procedures, in the first case by what is called distance matrix analysis, in the second by the procedure known as maximum parsimony analysis. Ribosomal RNA is a key and highly conserved molecule in the cell, being involved in the translation process, the process whereby genetic information is "translated" into enzymes and proteins. Therefore, it has retained in its sequence alignment a significant amount of historical information about various lineages. Dr. Woese has pioneered the development of molecular methods for phylogenetic analysis of bacterial genes and of bacterial evolution.