Image: Researchers from the Department of Microbiology at the University of Georgia discovered important genetic clues about the history of Archaea and the origins of life in a pioneering study in which they identified genes required for survival of Methanococcus maripaludis. Doctoral student and lead author Felipe Sarmiento found that roughly 30 percent of the nearly 1,800 genes in M. maripaludis are essential for survival. Many of these genes are homologous to eukaryotic genes that encode fundamental processes in replication, transcription and translation, providing direct evidence for a close relationship between Archaea and eukaryotes. These observations support the hypothesis that a portion of the eukaryotic cell was formed from components of an archaeon. The results of the study were published March 4 in the Proceedings of the National Academy of Sciences Early Edition and were performed with William Whitman, a professor in the Department of Microbiology and Jan Mrázek, an associate professor in the Department of Microbiology and the UGA Institute of Bioinformatics. Surprisingly, some of the genes that were classified as essential in M. maripaludis are unique to the Archaea. Of special interest, the gene polD, encoding a unique replicative DNA polymerase found in Archaea, was essential while the archaeal homolog of the ubiquitous DNA polymerase B was dispensable. These results show that PolD, rather than DNA polyermase B, is the major enzyme responsible for DNA replication in M. maripaludis. This represents a major paradigm shift as DNA replication has long thought to be one of the most conserved processes in living organisms. Interestingly, PolD is absent from the genomes of a group of Archaea known as the crenarchaeotes, suggesting a clear evolutionary division within the Archaea and an unanticipated variability in archaeal DNA replication. The observed differences in replication among the Archaea could be a direct consequence of formation of the lineages in an early stage of evolution before the replication system was fully formed. Alternatively, the differences observed in the replication mechanism may have evolved relatively late. If this is true, DNA replication may be more variable than thought in other groups of organisms. Go to http://news.uga.edu/releases/article/uga-researchers-shed-light-on-ancient-origin-of-life/ to read more about the study.
