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Second Stage Assembly

Second Stage assemblies are used to build plasmids out of multiple transcriptional units (Protocol found here). Occasionally this assembly can be used as a second step to building troublesome first stage plasmids - the first stage plasmid is assembled in a high copy/easier to work with backbone then moved to lower copy/more difficult to work with backbone. This assembly makes use of the BsmBI enzyme as described below.

Assembly reaction

Total volume will be 20 μL; you will need 10 fmol of each transcriptional unit plasmid for this assembly. Various backbones are regularly used in this step - if toxicity issues may be a factor, lower copy number vectors are recommended.

• 10 fmol of each transcriptional unit/backbone
• 2 μL of 10× T4 DNA ligase buffer (Promega)
• 1 μL of BsmBI
• 1 μL of T4 DNA ligase
• x μL water up to 20 μL total.

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Mix samples well by pipetting, then run the reaction on the thermocycler under the following conditions:

Step	Temperature	Time
1	42°C	1.5 min
2	16°C	3 min
Cycles 1-2:	Repeat 25x
3	50°C	5 min
4	80°C	10 min

• Transform 2 μL assembly reaction and plate recovery on LB + Selective Antibiotic

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-- Main.KateElston - 29 Jan 2018