MurrayRM:PURExpress system notes and experience

Notes on using the NEB PURExpress system.

Worked example: inducible expression

To illustrate how the system works, I am going to try various combinations of three different constructs:

• PLG1 (BBa_I2035) - GFP with a LacI-repressible promoter on a plasmid
• LLG2 (T7-Plac:RBS:GFP) - linear DNA with GFP on a LacI-repressible promoter, PCR'd from BBa_I2035
• LCL3 (T7:RBS:lacI) - linear lacI on a constitutive T7 promoter

In addition, I may build up an RFP-based construct, just in case I can't get access to BBa_I2035:

• PLR4 (T7-Plac:RBS:RFP) - plasmid DNA with RFP on a LacI-repressible promoter, PCR'd from the purified RFP plasmid (based on plasmids provided by Karsten Temme at UCSF) and inserted into Novagen pET vector. This can be used as a replacement for PLG1, if needed.

Naming scheme:

• L/P - DNA type: linear DNA versus plasmid
• C/L - promoter type: constitutive T7 promoter versus LacI-repressible
• G/L/R - coding region: GFP, RFP or LacI

Using these components, I can try out the following "circuits":

• GFP expression on a lacI-repressible T7 promoter (with no lacI => should flouresence): PLG1 or LLG2

This will allow a positive control to make sure that a T7 promoter with operator site still works

• Repression of GFP by lacI: PLG1/LLG2 + LCL3
• Induction of GFP using IPTG: PLG1/LLG2 + LCL3

DNA construction

Only the BBa_I2035 plasmid is in the form needed for use with the PURE system. The other sequences will be constructed using PCR-based editing.

PLG1

This construct is part of the biobricks library and will be obtained from freezer stocks at Stanford (e-mail to Drew on 12 Feb confirming existence).

LLG2

This is linear DNA containing a lacI-repressible T7 promoter in front of GFP, extracted from BBa_I2035 using a simple forward and reverse primer. Use of this piece of DNA allows testing of linear DNA versus plasmid DNA.

The sequence for the relevant section of BBa_I2035, starting from the beginning of the promoter and going through the end of the terminator

>BBa_I2035 Part-only sequence (856 bp) tcatacgactcactataggggaattgtgagcggataacaattcccctggatcctactagagtcacacaggaaagtactagatgcgtaaaggagaagaact tttcactggagttgtcccaattcttgttgaattagatggtgatgttaatgggcacaaattttctgtcagtggagagggtgaaggtgatgcaacatacgga aaacttacccttaaatttatttgcactactggaaaactacctgttccatggccaacacttgtcactactttcggttatggtgttcaatgctttgcgagat acccagatcatatgaaacagcatgactttttcaagagtgccatgcccgaaggttatgtacaggaaagaactatatttttcaaagatgacgggaactacaa gacacgtgctgaagtcaagtttgaaggtgatacccttgttaatagaatcgagttaaaaggtattgattttaaagaagatggaaacattcttggacacaaa ttggaatacaactataactcacacaatgtatacatcatggcagacaaacaaaagaatggaatcaaagttaacttcaaaattagacacaacattgaagatg gaagcgttcaactagcagaccattatcaacaaaatactccaattggcgatggccctgtccttttaccagacaaccattacctgtccacacaatctgccct ttcgaaagatcccaacgaaaagagagaccacatggtccttcttgagtttgtaacagctgctgggattacacatggcatggatgaactatacaaataataa tactagagctagcataaccccttggggcctctaaacgggtcttgaggggttttttg

• Forward primer: tcatacgactcactataggggaat
• Reverse primer: caaaaaacccctcaagacccgttt

LCL3

This sequence consists of lacI on a constitutive T7-promoter. It is constructed by doing PCR amplification of lacI out of a BBa_K091121 plasmid and then attaching the T7 promoter and RBS using the PURExpress universal primer. Sequence for lacI (from BBa_K091121 - wild type lacI):

>BBa_K091121 Part-only sequence (1083 bp) atgaaaccagtaacgttatacgatgtcgcagagtatgccggtgtctcttatcagaccgtttcccgcgtggtgaaccaggccagccacgtttctgcgaaaa cgcgggaaaaagtggaagcggcgatggcggagctgaattacattcccaaccgcgtggcacaacaactggcgggcaaacagtcgttgctgattggcgttgc cacctccagtctggccctgcacgcgccgtcgcaaattgtcgcggcgattaaatctcgcgccgatcaactgggtgccagcgtggtggtgtcgatggtagaa cgaagcggcgtcgaagcctgtaaagcggcggtgcacaatcttctcgcgcaacgcgtcagtgggctgatcattaactatccgctggatgaccaggatgcca ttgctgtggaagctgcctgcactaatgttccggcgttatttcttgatgtctctgaccagacacccatcaacagtattattttctcccatgaagacggtac gcgactgggcgtggagcatctggtcgcattgggtcaccagcaaatcgcgctgttagcgggcccattaagttctgtctcggcgcgtctgcgtctggctggc tggcataaatatctcactcgcaatcaaattcagccgatagcggaacgggaaggcgactggagtgccatgtccggttttcaacaaaccatgcaaatgctga atgagggcatcgttcccactgcgatgctggttgccaacgatcagatggcgctgggcgcaatgcgcgccattaccgagtccgggctgcgcgttggtgcgga tatctcggtagtgggatacgacgataccgaagacagctcatgttatatcccgccgttaaccaccatcaaacaggattttcgcctgctggggcaaaccagc gtggaccgcttgctgcaactctctcagggccaggcggtgaagggcaatcagctgttgcccgtctcactggtgaaaagaaaaaccaccctggcgcccaata cgcaaaccgcctctccccgcgcgttggccgattcattaatgcagctggcacgacaggtttcccgactggaaagcgggcagtga

• Round 1 forward primer: atgaaaccagtaacgttatacg
• Round 1 reverse primer: atgaaaccagtaacgttatacg
• Round 2 forward primer: PURExpress universal forward primer
• Round 2 reverse primer: same as round 1 reverse primer

PLR4

This is a linear sequence of DNA that can be used as a replacement for LLG2, in case I can't get BBa_I2035. In order to get this sequence, I have to insert RFP into a pET vector (has a lacI-repressible T7 promoter) and grow up some cells.

• Restriction enzymes to be used: TBD (waiting to find out which pET vectors we actually have available)