June 15 (UPI) — Scientists have discovered a microbe that uses two different translations of DNA, the world’s first.
The bilingual nature of the microbe makes it near impossible for scientists to predict which proteins its genome codes for.
DNA is composed of a sequence of four chemical bases, or nucleobases, represented by the letters A, T, C and G. Different sequences code for different combinations of nucleic acids, the building blocks of proteins, which fuel myriad biochemical processes inside the cells of all living organisms.
Three nucleobases, called codon, code for a single amino acid, and until now, scientists assumed the same three nucleobases always coded for the same amino acid.
But while studying the genomes of a unique group of yeasts, scientists realized they’d found an entirely different DNA language.
In most living organisms, the codon CTG codes for the amino acid leucine. Among the yeast, CTG was found to translate for serine in species and alanine in others. Scientists found one species, Ascoidea asiatica, randomly translates the codon into serine or leucine.
“This is the first time we’ve seen this in any species,” Laurence Hurst, director of the Milner Center for Evolution at the University of Bath, said in a news release.
Researchers described the novel microbe in the journal Current Biology.
“We were surprised to find that about 50 percent of the time that CTG is translated as serine, the remainder of the time it is leucine,” Hurst said. “The last rule of genetics codes, that translation is deterministic, has been broken. This makes this genome unique — you cannot work out the proteins if you know the DNA.”
When scientist investigated the biochemical mechanism behind the species’ random translation technique, they discovered two types of RNA, the molecules tasked with translating DNA’s codons.
“We found that Ascoidea asiatica, is unusual in having two sorts of tRNAs for CTG — one which bridges with leucine and one which bridges with serine,” said Martin Kollmar, from the Max-Planck Institute for Biophysical Chemistry in Göttingen. “So when CTG comes to be translated, it randomly picks one of the two tRNAs and hence randomly picks between serine and leucine.”
Researchers determined that the species’ random translation trait evolved 100 million years ago. Because serine and leucine are quite different, the trait is problematic. As such, Ascoidea asiatica has adapted by limiting expression of the codon CTG. The species closest relatives have all rid themselves of the potentially dangerous trait.
“It’s unclear why A. asiatica should have retained this stochastic encoding for so long. Perhaps there are rare occasions when this sort of randomness can be beneficial,” Kollmar said.