Year in review: Life’s complexity recoded

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Scientists made serious headway this year in tackling why life is both so darn complicated and so darn simple. Researchers upped life’s genetic complexity by coaxing a strain of the bacterium E. coli into using two synthetic genetic letters in addition to the standard four to build strands of DNA. Another team took a minimalist approach, creating a pared-down version of a yeast chromosome.

“These are big achievements,” says Ross Thyer of the University of Texas at Austin. Future work may produce unforeseen engineering marvels, he says.

The researchers working with E. coli added two new molecular building blocks to the four that make up the rungs in DNA’s double helix. Ordinary DNA building blocks, or bases, pair up to connect DNA’s two helical strands. In the E. coli, the two artificial bases, the awkwardly named d5SICS and dNaM, paired up to form a new rung in the helix (SN: 6/14/14, p. 14). The feat may help scientists understand why the standard double helix is so simple.

“Why don’t we have more base pairs in nature?” asks Thyer. Every living thing uses the same genetic alphabet to transmit information from one generation to the next. These few building blocks yield incredible diversity, from earthworms to human beings.

Other researchers this year took a different approach: simplifying a relatively complicated life-form. The team, which included a small army of college students, assembled a synthetic yeast chromosome and showed that it works fine in living yeast cells (SN: 5/3/14, p. 7). At 272,871 base pairs long, the synthetic chromosome is a streamlined version of the 316,617–base pair original. Although scientists have built bacterial genomes from scratch (SN: 6/19/10, p. 5), the yeast chromosome is the first step in building a synthetic genome of a eukaryote, an organism, such as a human, that stores its DNA in a nucleus.

When yeast’s other 15 chromosomes are synthesized, scientists will be closer to understanding what’s essential for making a complicated living thing. “It’s an excellent way to understand the minimal components required for the complexity of life,” Thyer says.