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Fig. 4 | BMC Biology

Fig. 4

From: Layering genetic circuits to build a single cell, bacterial half adder

Fig. 4

Design and characterisation of the biological NIMPLY gate. a Genetic blueprint and logic output of NIMPLY gate. The NIMPLY gate is designed by incorporating synthetic lambda repressor binding sites downstream of OR gate promoters and regulating the expression of lambda repressors through the pBAD promoter. RFP is expressed only in the presence of input B, rhamnose. b Characterisation of NIMPLY gate with different ribosome binding sites. At steady state NIMPLY gate which utilizes a weaker ribosome binding site (RbsB) directly upstream of the RFP reporter (denoted by crosses, stars and circles) exhibits better control and reduced expression leak, as compared to the NIMPLY gate design that contains a stronger ribosome binding site (denoted by diamonds, squares, and triangles). Expression leakiness in circuits with strong and weak ribosome binding sites after 4 hours are denoted by green and orange arrowheads, respectively. Constructs that were singly induced with input B, induced with both inputs A and B, and uninduced are represented by R, A + R and NC as shown. c Characterisation of NIMPLY gates with two (blue circles) and four (orange squares) lambda repressor binding sites. The black line represents empirically derived transfer function for the construct with dual lambda repressor binding sites, as described by the equation provided. Constructs were induced with a fixed amount of rhamnose (input B) and titrated with various concentrations of arabinose (input A). An increased number of repressor binding sites disrupted the NIMPLY gate, possibly due to pronounced effect of 5′ mRNA secondary structures. Error bars represent standard deviation of three independent experiments

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