Design of the system
Of course, recording one changing signal in only two time periods is not enough for us to solve real-world problems. As a result, we have further designed multi-signal system based on two-signal system, which records one changing signal in more than two time periods.
Overview of the whole circuit
Like two-signal system, multi-signal system is composed of three parts, logic gates, sequential memory structures and basic orthogonal memory modules(Fig.1). The main difference between two systems is the sequential memory structures. Due to the diversity and orthogonality of serine integrases, much more orthogonal integrases used in sequential memory structures and basic orthogonal memory modules can be involved in this extending system.
Sequential memory structures
Fig.2 shows the sequential memory structures of multi-signal system(three-signal system). Not mentioned before, attB/P sites of integrases have core sequences. By mutating these sequences, orthogonal sites of one integrase can be made, which means that one integrase may control inversion of two sites, and that there can be little cross-talk. It helps to design this part, which has shown in the same color but in different shape. Other features of this circuit is similar to the two-signal system. It can be extended just by copying and pasting the design, involving more orthogonal integrases.