Davidson College Department of Biology Honors Thesis Title ...

as one repression binding site that is specific to either the las or the lux system. In order
to make the promoters solely responsive to the input of autoinducer molecules, LuxR and
LasR would need to be constitutively expressed via a genomic insertion (Waters and Bassler,
2005).
Figure 3: Design of XOR Gate. Each promoter contains two binding regions, one for activation
(green box) and one for repression (red box). Promoter repression overrides activation. LuxR
and LasR are constitutively expressed by the bacterial genome, and 3OC6 and 3OC12 are the two
inputs to the system.
If neither 3OC6 nor 3OC12 is present in the cell, both promoters should be constitutively off
since they lack the activation signal. If exactly one of the autoinducer molecules is present,
one of the two promoters should be turned on and the other promoter should be repressed.
If both autoinducers are present, then repression is expected to override activation, keeping
both promoters off. In this way, XOR logic determines the transcriptional state of an output
gene based on two molecular inputs.
Implementing a Simple Hash Function
An XOR gate could be applied to many types of larger systems, and our lab envisioned using
it to implement a bacterial hash function. A hash function is a mathematical procedure that
converts digital information of any length into a fixed-length “hash value.” Hash functions
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