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From 2013.igem.org

Need to be re-writen.
For the silk to be secreted the sec pathway is used. In using this pathway Signal Sequences are needed. this allows the bacillus to recognize the protein as something that needs to be moved to the outside of the cell.
The first Signal sequences that will be atempted are MotB FliZ EstA and LytB.

Introduction

We are employing the Gram-positive model bacterium Bacillus subtilis to secrete silk. B. subtilis is
generally regarded as safe (GRAS) and is often used in industry for the commercial production of extracellular
proteins because proteins only need to traverse a single membrane.

To distinguish extracellular proteins from cytoplasmatic proteins, extracellular proteins are provided with a
cleavable aminoacid signal peptide (SP).

B. subtilis protein translocation machinery.

Figure 1. Schematic overview of the B. subtilis protein translocation machinery. The signal recognition particle (SRP)
consists of scRNA, Ffh and HBsu. See text for details. The dashed line arrow indicates an SRP-independent pathway,
possibly mediated by SecA that shuttles between the SecYEG-bound and free cytosolic state. Proteases that degrade
the secreted proteins are located near the membrane surface, in the cell wall and free in the suspending medium.

KH van Wely et al. 2006 (FEMS Micro. Rev.)