Difference between revisions of "Part:BBa K2918002"

Revision as of 23:19, 18 October 2019

Φ29 Single Stranded Binding Protein (SSB/p5)

Single Stranded Binding protein of the Φ29 bacteriophage

Sequence and Features

The part has been confirmed by sequencing and there are no mutations.

Usage and Biology

The Φ29 replication mechanism involves replication of a protein-primed based replication linear DNA. Protein primed replication, unlike the conventional DNA or RNA primed mechanism, do not depend on specific sequences of DNA/RNA and simplifies the design of replication systems. The Φ29 replication can be established by using four simple proteins: Φ29 DNA polymerase ( (DNAP/p2) (TP/p3), single stranded binding protein (SSB/p5) and double stranded binding protein (DSB/p6). The replication process begins by binding of the Φ29 DNA polymerase and terminal protein complex at the origins of replication (OriL and OriR), which flank the protein-primed linear plasmid (Nies et al., 2018). The double stranded DNA binding proteins (DSB/p6) aid in the process of replication and bind more intensely at the origins of replication (OriL and OriR), destabilizing the region and facilitating strand displacement. Single stranded binding proteins bind to the displaced DNA strand preventing strand switching of the DNA polymerase and protecting the linear plasmid from host nucleases (Nies et al., 2018). The replication mechanism is depicted in Figure 1.

The Φ29 replication system is promising in many ways:

• The Φ29 DNA Polymerase has the highest processivity of all known single subunit DNA polymerases (Blanco et al., 1988), and can be used for whole genome amplification.
• The Φ29 machinery along with cell free expression systems can be used to establish the three dogmas of biology in-vitro. Setting the basis for artificial cell development.
• The existing DNA-protein covalent bonds offer many possibilities to engineer the terminal proteins with functional peptide sequences.
• We envision that the unique configuration of the double-stranded, protein-capped linear replicon will be a basis for many new engineered protein-DNA complexes.
• Orthogonal replication not only enables replication independent from the host, but the ability to engineer the orthogonal DNA polymerase’s fidelity without introducing mutations in the cell’s genome makes in vivo directed evolution a possibility.

Characterization

to be edited

Strain Construction

The DNA sequence of the part was synthesized by IDT with flanking BpiI sites and respective MoClo compatible coding sequence overhangs. The part was then cloned in a level 0 MoClo backbone pICH41308 and the sequence was confirmed by sequencing. The cloning protocol can be found in the MoClo section below.

Modular Cloning

Modular Cloning (MoClo) is a system which allows for efficient one pot assembly of multiple DNA fragments (Weber et al, 2011). The MoClo system consists of Type IIS restriction enzymes that cleave DNA 4 to 8 base pairs away from the recognition sites. Cleavage outside of the recognition site allows for customization of the overhangs generated. The MoClo system is hierarchical. First, basic parts (promoters, UTRs, CDS and terminators) are assembled in level 0 plasmids in the kit. In a single reaction, the individual parts can be assembled into vectors containing transcriptional units (level 1). Furthermore, MoClo allows for directional assembly of multiple transcriptional units. Successful assembly of constructs using MoClo can be confirmed by visual readouts (blue/white or red/white screening). For the protocol, you can find it here.

Note: The basic parts sequences of the Sci-Phi 29 collection in the registry contain only the part sequence and therefore contain no overhangs or restriction sites. For synthesizing MoClo compatible parts, refer to table 2. The complete sequence of our parts including backbone can be found here.

Table 1: Overview of different level in MoClo

For synthesizing basic parts, the part of interest should be flanked by a BpiI site and its specific type overhang. These parts can then be cloned into the respective level 0 MoClo parts. For level 1, where individual transcriptional units are cloned, the overhangs come from the backbone you choose. The restriction sites for level 1 are BsaI. However, any type IIS restriction enzyme could be used.

Table 2: Type specific overhangs and backbones for MoClo. Green indicates the restriction enzyme recognition site. Blue indicates the specific overhangs for the basic parts

References

• Nies, P. Van, Westerlaken, I., Blanken, D., Salas, M., Mencía, M., & Danelon, C. (n.d.). Self-replication of DNA by its encoded proteins in liposome-based synthetic cells. Nature Communications, (2018), 1–12. https://doi.org/10.1038/s41467-018-03926-1
• Blanco, L., Bernads, A., Lharo, J. M., Martins, G., & Garmendia, C. (1989). Highly Efficient DNA Synthesis by the Phage 429 DNA Polymerase.
• Weber, E., Engler, C., Gruetzner, R., Werner, S., & Marillonnet, S. (2011). A Modular Cloning System for Standardized Assembly of Multigene Constructs. Plos ONE, 6(2), e16765. doi: 10.1371/journal.pone.0016765