Latest revision as of 04:00, 2 November 2017

Plasmid partitioning system (SynORI framework)

SynORI framework gives the opportunity to have low copy plasmid groups, yet in order for them not to be lost during cell division, there must be a mechanism that actively keeps plasmids in the cell.

This particular biobrick encodes low-copy plasmid partitioning system, designed specifically to stabilize SynORI (multi-plasmid system, read more here <link>) low copy plasmid groups, but can also be used to stabilize any type of plasmid.

Sequence and Features

Introduction

Biology

Figure 1. Segregation system in action

Par region derived from pSC101 is a lot different from its counterparts, for example, F and P1 plasmids (Meacock and Cohen 1980). It does not seem to encode any protein but contains a binding site for DNA gyrase (Wahle and Kornberg 1988). In contrast, both F and P1 systems encode partitioning proteins in plasmids making Par regions as big as 2kb.

Plasmids with partial deletions of par in pSC101 have decreased negative supercoiling and are extremely unstable (lost from cells in a short amount of time). This has led to the proposal that gyrase-generated negative supercoiling establishes a DNA conformation which enables plasmids to interact with E. Coli structures which distribute them to daughter cells at division (Miller et al., 1990).

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]!

Active segregation system in SynORI

SynORI framework gives the opportunity to have low copy plasmids, but in order for them to be stable (to not lose plasmids from the cell during cell division) there must be a mechanism that actively keeps plasmids in the cell.

This is where active segregation system comes in. When building a specific synthetic origin of replication, this DNA sequence can be added to stabilize the plasmid group.

Characterization of plasmid partitioning system (Vilnius-Lithuania 2017)

Measurement of Par⁺ and Par ^- pSB4A5 stability

Since we are cloning the partitioning system from pSB4A5, we must first make sure that our target sequence is ensuring the stability of pSB4A5 plasmids. We have deleted the partitioning sequence by using two blunt end restriction enzymes, ligating the vector and cutting the correct size vector (without the partitioning sequence) from gel after agarose electrophoresis.

We have then performed a stability experiment by using two plasmids - the original Par+ pSB4A5 and our Par- mutant.

Figure 2.pSB4A5 plasmid copy number with and without PAR

Figure 2 - results from the first experiment where plasmid loss was evaluated using low copy BioBrick standard vector pSB4A5 + mRFP. A significant decrease in number of plasmid-containing cells is visible when active partitioning system is missing and plasmid number decrease is not visible during 100 generations period.

Figure 3

Figure 3. A. Plates of transformants containing vector with active partitioning system after 20 generations. LB plates without antibiotic - left side. LB plates with ampicillin - right side. B. Plates of transformants containing vector without active partitioning system after 20 generations. LB plates without antibiotic - left side. LB plates with ampicillin - right side. C. Plates of transformants containing vector with active partitioning system after 100 generations. LB plates without antibiotic - left side. LB plates with ampicillin - right side.D. Plates of transformants containing vector without active partitioning system after 100 generations. LB plates without antibiotic - left side. LB plates with ampicillin - right side.E. After 200 generations cells were spread once again to see mRFP intensity decrease*, compared to the previous generations the number of mRFP containing colonies without active partitioning system is invisible, the intensity of mRFP of the transformants with active partitioning system is significantly decreased.

• It is possible to evaluate plasmid-containing colonies by checking if the colony contains mRFP. However, it might be tricky since the intensity can be slightly visible in colony, in that case patching bacteria on LB plates is a more trustworthy method.

References