Revision as of 02:06, 2 November 2017

Rop protein with anderson (0.24) promoter for global plasmid copy number control

When placed in a SynORI system this device lowers plasmid copy number of each group as it can bypass the selective control. It consists of a weak Anderson promoter, weak Anderson RBS, ROP protein and a double terminator.

Device also works with other plasmids consisting of ColE1 origin of replication

Devices from the same series that have different Anderson promoters: part:BBa_K2259072 (0 Anderson), part:BBa_K2259073 (0.15 Anderson), part:K2259074 (0.24 Anderson).

See how this part fits into the whole SynORI framework by pressing here!

Sequence and Features

Figure 1. Main principles of ColE1 plasmid family replication. Rop protein interaction region marked in red square. (Citation needed)

Introduction

Biology

Repressor of primer (ROP) is a small dimeric protein that participates in ColE1 plasmid family copy number control, by increasing affinity between two complementary RNAs - RNA I (Replication inhibitor) and RNA II (Replication activator) (Fig. 1). ^[1] By increasing affinity of the two RNA molecules, Rop decreases the rate of plasmid replication initiation events.

Figure 2. Structure of the ColE1 Rop protein, at 1.7 angstroms resolution.^[2]

Rop dimer is a bundle of four tightly packed alpha helices that are held by hydrophobic interactions (Fig. 2).

Usage with SynORI (Framework for multi-plasmid systems)

About SynORI

SynORI is a framework for multi-plasmid systems created by Vilnius-Lithuania 2017 which enables quick and easy workflow with multiple plasmids, while also allowing to freely pick and modulate copy number for every unique plasmid group! Read more about [http://2017.igem.org/Team:Vilnius-Lithuania SynORI here]!

This device in SynORI

This is a constitutive global copy number modulator device which lowers plasmid copy number of every group in the system bypassing the selective control of different groups. These constitutive devices can be used with different Anderson promoters to select a different copy number.

Devices from the same series that have different Anderson promoters: part:BBa_K2259072 (0 Anderson), part:BBa_K2259073 (0.15 Anderson), part:K2259074 (0.24 Anderson).

See the [http://2017.igem.org/Team:Vilnius-Lithuania Vilnius-Lithuania 2017 team wiki] for more insight about our synthetic origin of replication (SynORI).

Further details

For more background information and indepth insight on this part's design please see the individual part page of ROP proteinpart:BBa_K2259010.

Characterization of Rop protein (Vilnius-Lithuania 2017)

Rop expression

Figure 3. SDS-PAGE of Rop protein induction. M – Thermo Scientific PageRuler Unstained Low Range Protein Ladder; 1 – E. coli soluble proteins fraction without induction after 7 h of growth; 2-5 – cells induced using 1 mM IPTG – hours above tracks indicate different time of growing after induction.

We have first decided to verify the expression of Rop protein to make sure that our designed Rop gene gives appropriate mRNA which is translated in the cell correctly. Rop gene was then placed under inducible T7 promoter. After two hours of growth, E. coli DH5α cells containing plasmid with Rop gene were induced using 1 mM IPTG. Soluble proteins from the cell lysates were separated by centrifugation and then used for SDS-PAGE. Size of Rop protein is 7,5 kDa, so it can be seen below 10 kDa size standard mark. Figure 3 shows, that Rop protein was induced successfully and its quantity increases by prolonging cell growth. It is found in soluble protein fraction which strongly suggests that Rop protein possibly forms an active spatial structure in vivo and might influence RNA I-RNA II duplex formation.

Constitutive Rop protein effect on plasmid copy number

We have then wanted to see if we can add a constitutive Anderson promoter to Rop gene in order to change the copy numbers of a plasmid group. We have cloned 3 different Anderson promoters next to Rop gene and then moved it next to RNA I. We then moved these 3 intermediate parts (part:BBa_K2259072, part:BBa_K2259073, part:BBa_K2259074) into the minimal SynORI vector (part:BBa_K2259092) next to RNA II (part:BBa_K2259075, part:BBa_K2259053, part:BBa_K2259052). We have then calculated the plasmid copy number.

Figure 4. SynORI constitutive global copy number device with Rop under different strength Anderson promoters.

As seen in in the Figure 4, our Rop protein constructs successfully lower the plasmid copy number. Each Anderson promoter increases Rop concentration and consequently, lowers plasmid copy number.

Inducible Rop protein effect on plasmid copy number

We have also investigated Rop protein with inducible Rhamnose promoter in order to have a viable option of inducible copy number control. We have cloned Rop gene next to Rhamnose promoter and RNA I (BBa_K2259070) and then placed this construct next to RNA II (part:BBa_K2259076) in SynORI minimal vector (part:BBa_K2259092).

Figure 5. SynORI inducible global copy number device with different rhamnose concentrations.

These results show that Rhamnose promoter is too strong for Rop protein expression, because even the leakage of promoter at 0 percent induction leads to copy decrease to average 1 copy per cell. That means that cells can barely survive and if they do, the inhibition level is so high they cannot maintain more than one plasmid.

Despite the high expression level this device can still prove to be useful in the future, for example if characterized with an active partitioning system this construct could become a useful tool for extremely low copy plasmid group generator.

Rop protein as global regulator

As a proof of concept different groups of SynORI devices were placed in a cell by co-transformation. SynORI global copy number control devices (part:BBa_K2259072 (0 Anderson), part:BBa_K2259073 (0.15 Anderson), part:K2259074 (0.24 Anderson)) together with B-GC SynORI device (BBa_K2259078) and (part:BBa_K2259072 (0 Anderson), part:BBa_K2259073 (0.15 Anderson), part:K2259074 (0.24 Anderson)) with D-GC SynORI device (BBa_K2259079).

Figure 6.SynORI A device with Rop under different Anderson promoters together with SynORI B-GC device.

Figure 7.SynORI A device with Rop under different Anderson promoters together with SynORI D-GC device.

As can be seen in Figure 6. and Figure 7. Rop protein placed in a single plasmid lowered the plasmid copy number of both plasmid groups, this proves that Rop protein works by binding to a kissing-loop complex and bypass the individual control of different groups. It can also be concluded that RNA II A and RNA II B act as different ORIs and does not inhibit the replication of each other

References

1. ↑ Castagnoli L, Scarpa M, Kokkinidis M, Banner DW, Tsernoglou D, Cesareni G. Genetic and structural analysis of the ColE1 Rop (Rom) protein. The EMBO Journal. 1989;8(2):621-629.
2. ↑ Banner DW, Kokkinidis M, Tsernoglou D. Structure of the ColE1 Rop protein at 1.7 Å resolution. J Mol Biol. 1987 m.;196(3):657–75.