February 25, 2005
The Ancient Splice of Life
One of the key motivations for revisiting the probability of life elsewhere in the universe is the surprising proclivity of life in hostile places on Earth. New findings suggest that modern organisms may have useless DNA fragments today that once saved their ancestors lives in extreme environments.
Astrobiology Magazine -- Yale scientists report in the journal Nature that the "missing" genes for tRNA in an ancient parasite are made up by splicing together sequences in distant parts of the DNA genome.
The research led by Professor Dieter Söll in the Department of Molecular Biophysics and Biochemistry at Yale focuses on the most ancient organism with a known genome sequence.
Nanoarchaeum equitans, is a member of a new phylogenetic kingdom in the Archaea containing organisms that are primitive, parasitic and extremophile, or notable for living in the most extreme environments.
Surprisingly, Söll's team found that, although the genome of Nanoarchaeum lacks several intact tRNA genes, functional forms of those tRNAs can be made by copying from two distant DNA sequences -- and joining them.
The regions on the separate pieces, that allow them to find each other and splice, are somewhat similar to internal sequences found in tRNA genes of more complex organisms.
These regions, termed introns, are sequences that are cut out of whole gene transcripts during the process of tRNA maturation. The known tRNA introns in organisms like yeast, however, appear to have no function. Therefore, modern tRNA introns might be remnants of an old essential process of tRNA biosynthesis.
"These results may point to extremophiles in the kingdom of Archaea as predecessors of more modern organisms that have gained a genetic load in the process of evolution," said Söll. "Or they may represent a specialization that has rid itself of genetic baggage to exist in extreme environments."
Understanding how primitive organisms like Nanoarchaea operate gives clues to -- but not proof of -- the relationship between modern and ancient organisms.
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