Engineering a bacterial tape recorder.

A method has been developed to produce and integrate single-stranded DNA into genomic locations in bacteria in response to exogenous signals. The system functions similarly to a cellular tape recorder by writing information into DNA and reading it at a later time. Much like other cellular memory platforms, its operation is based on DNA recombinase function. However, the scalability and recording capacity have been improved over previous designs. In addition, memory storage was reversible and could be recorded in response to analogue inputs, such as light exposure. This modular memory writing system is an important addition to the genomic editing toolbox available for synthetic biology.

Optically Controlled Signal Amplification for DNA Computation.

The hybridization chain reaction (HCR) and fuel-catalyst cycles have been applied to address the problem of signal amplification in DNA-based computation circuits. While they function efficiently, these signal amplifiers cannot be switched ON or OFF quickly and noninvasively. To overcome these limitations, a light-activated initiator strand for the HCR, which enabled fast optical OFF → ON switching, was developed. Similarly, when a light-activated version of the catalyst strand or the inhibitor strand of a fuel-catalyst cycle was applied, the cycle could be optically switched from OFF → ON or ON → OFF, respectively. To move the capabilities of these devices beyond solution-based operations, the components were embedded in agarose gels. Irradiation with customizable light patterns and at different time points demonstrated both spatial and temporal control. The addition of a translator gate enabled a spatially activated signal to travel along a predefined path, akin to a chemical wire. Overall, the addition of small light-cleavable photocaging groups to DNA signal amplification circuits enabled conditional control as well as fast photocontrol of signal amplification.

Interfacing synthetic DNA logic operations with protein outputs.

DNA logic gates are devices composed entirely of DNA that perform Boolean logic operations on one or more oligonucleotide inputs. Typical outputs of DNA logic gates are oligonucleotides or fluorescent signals. Direct activation of protein function has not been engineered as an output of a DNA-based computational circuit. Explicit control of protein activation enables the immediate triggering of enzyme function and could yield DNA computation outputs that are otherwise difficult to generate. By using zinc-finger proteins, AND, OR, and NOR logic gates were created that respond to short oligonucleotide inputs and lead to the activation or deactivation of a split-luciferase enzyme. The gate designs are simple and modular, thus enabling integration with larger multigate circuits, and the modular structure gives flexibility in the choice of protein output. The gates were also modified with translator circuits to provide protein activation in response to microRNA inputs as potential cellular cancer markers.

Modulating the pKa of a tyrosine in KlenTaq DNA polymerase that is crucial for abasic site bypass by in vivo incorporation of a non-canonical amino acid.

It is estimated that about 10,000 abasic sites are formed per day per cell. Abasic sites impose a significant challenge for bypass synthesis by DNA polymerases. Recently, a tyrosine in KlenTaq DNA polymerase has been highlighted as being crucial for nucleotide selection opposite abasic sites. Structural data indicated a hydrogen bond between the tyrosine's hydroxy group and the N3 of an incoming ddATP opposite the abasic site. In order to further investigate abasic site bypass, we incorporated the unnatural amino acid 2,3,5-trifluorotyrosine at the position of the crucial tyrosine of KlenTaq DNA polymerase. Fluorine substitution at the tyrosine decreased the pka value of the tyrosine's hydroxy group and allowed its protonation state to be modulated. Single-nucleotide-incorporation experiments revealed reduced activity for the KlenTaq mutant compared to the wild-type when bypassing an abasic site analogue. The finding stresses the involvement of this tyrosine and its hydrogen bonding in abasic site bypass.