Researchers develop new tool for making genetic engineering of microbial circuits reliably predictable

Fluorescence microscopy images of cells containing various plasmid pairs which were constructed with the help of a tna element adaptor and logic gates driven by two, three or four RNA inputs that linked to ribosome binding sites.

(Phys.org)Synthetic biology is the latest and most advanced phase of genetic engineering, holding great promise for helping to solve some of the world's most intractable problems, including the sustainable production of energy fuels and critical medical drugs, and the safe removal of toxic and radioactive waste from the environment. However, for synthetic biology to reach its promise, the design and construction of biological systems must be as predictable as the assembly of computer hardware.

An important step towards attaining a higher degree of predictability in synthetic biology has been taken by a group of researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) under the leadership of computational biologist Adam Arkin. Arkin and his team have developed an "adaptor" that makes the genetic engineering of microbial components substantially easier and more predictable by converting regulators of translation into regulators of transcription in Escherichia coli. Transcription and translation make up the two-step process by which the coded instructions of genes are used to synthesize proteins.

"Application of our adaptor should produce large collections of transcriptional regulators whose inherent composability can facilitate the predictable engineering of complex biological circuits in microorganisms," Arkin says. "This in turn should allow for safer and more efficient constructions of increasingly complex functions in microorganisms."

Arkin is the director of Berkeley Lab's Physical Biosciences Division and the corresponding author of a paper describing this work in Nature Methods. The paper is titled "An adaptor from translational to transcriptional control enables predictable assembly of complex regulation. Co-authoring this paper were Chang Liu, Lei Qi, Julius Lucks, Thomas Segall-Shapiro, Denise Wang and Vivek Mutalik.

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When a bacterial translational regulator is fused to a tna element adaptor, it is able to also regulate transcriptional elongation.

"Much of the regulatory potential of a bacterium is contained in the five-prime untranslated regions (UTRs), which control the expression of physically adjacent downstream genes and have become attractive platforms for a parts-based approach to synthetic biology," Arkin says. "This approach, in which integrated engineered regulatory parts respond to custom inputs by changing the expression of desired genes, must satisfy two criteria if it is to have long-term success. First, the regulatory parts must be easily engineered in a way that yields large homogenous sets of variants that respond to different custom inputs, and second, the parts must be composable such that they can be easily and predictably assembled into useful higher-order functions."

In the five prime UTRs of bacteria, two primary types of regulators can serve as starting points for designing new parts those that regulate transcriptional elongation, in which cellular inputs are linked to the process by which a sequence of DNA nucleotides is transcribed into a complementary sequence of RNA; and those that regulate translation, in which a ribosome translates the RNA message into a protein. Transcriptional elongation regulators meet the second criterion by featuring versatility and composability that makes them ideal for building custom regulatory functions. Translational regulators meet the first criterion by being easier to engineer and relatively common to all bacteria.

"Our solution for meeting both criteria was to develop an adaptor based on tryptophanase, the catabolic operon for tryptophan that converts regulators of translational initiation into regulators of transcriptional elongation," Arkin says. "Because our adaptor strategy bypasses the otherwise restrictive tradeoff between criterion one and criterion two, we believe it will have a crucial role in the long-term development of five prime UTRs as platforms for the design and integration of custom regulatory parts."

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Researchers develop new tool for making genetic engineering of microbial circuits reliably predictable