Team:MIT phage design


hairy cells and polymerizing phage - design

We envision a phage material composed of polyphage strands, produced by cells that carry hyperphage. In addition to producing all the proteins to form the polyphage, each cell will produce a p8-fusion from a separate plasmid to be displayed on the polyphage coat. The polyphage strands cross-link with one another via the coiled-coil interactions of proteins displayed on the phage coat.

We designed the phage material formation module to be integrated with the UV controller module. Our fusion protein is controlled by the toggle, allowing linkage to occur only where UV light has set the state of the toggle to low CI/ high LacI. p3 is under control of an inverter such that where UV light has set the state of the toggle to low CI/ high LacI, there is no p3 production, and thus polyphage formation.

Hyperphage is a commercially available version of M13 with the gene for pIII truncated. Recall that pIII is required for the termination of assembly and exit from the host cell membrane, and thus hyperphage can be used as a polyphage "generator." Hyperphage can be obtained from Progen Biotechnik in Germany. Below you can see a hyperphage plasmid map next to a M13 KO7 plasmid map. Notice the size difference in the green highlighted gIII gene (gIII produces pIII).


Above is the genetic design of our fusion construct.

p8 was chosen to "carry" our linker coil. Since repeating copies of p8 makes up the vast majority of the surface area of the phage, more fusion proteins are likely to be displayed (recall that in single phage, p8 is present in 2700 copies, compared to p9's 5 copies. The proportion is even more drastic in polyphage). The specific protein used, "opti-p8" is a mutational analysis-derived version that has been shown to incorporate fusion proteins into the phage coat at a higher efficiency (Weiss et al. 2000).

The p8 leader sequence is responsible for localization of p8 to the membrane, where it is cleaved and the protein is allowed to be incorporated into the phage. We took the first 27 amino acids from M13 strain M13KE.

In between the coil and the p8 protein are the "tag" and the "linker" sequence. The tag was introduced to facilitate western blotting experiments, and is either an HA tag or a Myc tag, depending on the coil. Like the choice of "opti-p8," the "linker" sequence was chosen because of its property of higher fusion incorporation efficiency.

For additional information about the fusion design, please see this PDF. This construct can be easily assembled with BioBrick assembly into the circuit described below.


  1. Toggle - The toggle-switch works by mutual repression. Through addition of IPTG, it can be set to “off”, and UV, “on”. The “on” state lets RecA cleave cI, allowing for leaky transcription from the hybrid luxR/cI-regulated promoters. For full transcription, the LuxR-AHL complex must bind. AHL can thus be added to induce transcription while LuxR is produced constitutively. This toggle was donated from the Collins lab. It has been biobricked as K415300 (a low-power version is K415301).

  2. & 3. Pattern Formation - Constitutive LuxR allows for expression of mCherry and pVIII fusion proteins where there is no cI (i.e., where there is UV induction). Two distinct pVIII phage proteins are expressed in two populations of cells which then should bind together via leucine zipper interactions to allow for polymerization in the UV-induced area. Part (2) is K415010, Part (3) combined with Part (2) creates our K415147-152 parts.

  3. Inverter - In order to inhibit phage polymerization outside of the UV-induced region, an inverter allows for transcription only in areas where UV has not been introduced. pIII production then prohibits polyphage from forming which precludes leucine zipper interactions and polymerization. This part is currently in the construction phase and has not been incorporated into existing circuitry. (There's also another inverter being developed using the CymR system.)

Background       Construction