Biology

Biology Research Areas

Group I Self-Splicing Introns - Sandra A. Nierzwicki-Bauer

The question of life's origins is one of the oldest and most difficult in biology. The answer, if ever known, will not be a single statement of fact but rather an extended chronology, beginning with the formation of the Earth and ending with the appearance of cellular organisms. This problem is confounded because there is little direct evidence of the events that occurred during roughly the first thousand million years of Earth's history. The oldest rocks that provide clues regarding life's origins are 3.6 x 109 years old, and by that time cellular life seems already to have been well established. However, remnants of ancient organisms may be found in the form of "molecular fossils" within the genomes of modern organisms. One such candidate might be self-catalytic RNA molecules which can serve as hereditary molecules as well as exhibit some properties of proteins. The discovery of self-catalytic RNA of molecules has lead to a revival of interest in the idea that there was a time, before the origin of protein synthesis, when life was based entirely on RNA. One such class of catalytic molecules are the Group I self-splicing introns.

A controversial issue, which remains unsolved, is whether introns are ancient features of gene structure ('introns early') or whether introns are more recently acquired elements obtained through horizontal gene transfer ('introns late'). In support of the more recent acquisition of introns is evidence that some introns are mobile elements. However, the intron early view suggests that introns were present in the earliest progenitors of modern cells and there has been a trend in some organisms to lose introns, thus streamlining their genome and allowing for more rapid growth and response to environmental factors. A class of introns, called Group I introns, which are located in the tRNA genes of chloroplasts of higher plants, bacteriophages and viruses, archaebacteria, and recently in certain eubacteria (a- and b-proteobacteria; cyanobacteria) lends support to the ancient origin of these sequences.

Work in our lab is being carried out to enrich our knowledge as to the abundance, distribution and diversity of Group I self-splicing introns in phylogenetically diverse bacterial species. For our studies on Group I introns, we are using isolates from deep subsurface soils, that provide a unique, previously unstudied group of organisms. Further, since it is possible that some of these bacteria are descendants from bacterial species present at the time of sediment deposition, they may serve as a "living molecular fossil". State-of-the-art molecular techniques including PCR and development and utilization of oligonucleotide probes are being used for this research.

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