Figure 6. Modularity of the AND gate.

Figure 6. Modularity of the AND gate.

The modularity of the AND gate is demonstrated by reconnecting the gate to new inputs (natural promoters), and a new output (desired phenotype).

A. Exchanging the inputs: Input 1: The lux promoter, which responds to the quorum signal AI-1. Input 2: The mgrB promoter, which responds to the absence of exogenous magnesium via the PhoPQ two-component system. Only when both promoters are on (in the presence of AI-1 and magnesium limitation) is the output on.

B. Exchanging the output for the inv gene, coding for invasin, a protein that allows bacteria to invade mammalian cells. When both input promoters are on (in the presence of Sal and magnesium limitation), the cells exhibit the same level of invasiveness as if the cells were programmed with the inv gene placed under a constitutive promoter.

(Image from Figure 6 of Anderson et al., 2007. Permission pending.)