Sequential logic circuit built on λ exonuclease for cross inhibition

Abstract

The output state of a sequential logic circuit is determined by both the input signal at that time and the original state of the circuit, so the ability of the sequential logic circuit to unveil history-dependent signals will contribute to our understanding of the ordered expression of genes. Here, we show a sequential logic circuit built on λ exonuclease, capable of detecting the relative sequence between inputs and inhibiting the second signal response when the first signal activates the corresponding output signal. The input can be used not only as an active signal but also as a control signal to activate the component of the λ exonuclease built to generate an inhibit strand, enabling cross-inhibition. The hydrolytic properties of λ exonuclease allow for orthogonal sequence design, which enables flexibility in sequence design. It has been experimentally demonstrated that λ exonuclease itself is catalytic and that a small amount of input can still provide good inhibition with the assistance of λ exonuclease. The sequential logic circuit we have designed can be modularly integrated into larger-scale circuits, to handle input sequence-related functions and lay the foundation for further understanding of ordered gene expression.